The purpose of research is to increase the ore mass extraction ratio when mining rich iron ores by changing the shape of the stope chamber, as well as to substantiate its stable parameters under the conditions of the rock pressure manifestation. Used in mines existing methodologies for determining the structural elements of mining system are based on calculated equivalent spans of outcropping the stope chambers, which have a rectangular or tent shape. For the first time using the ANSYS software package, it has been determined that the formation of a compensation chamber of quasi-parabolic shape can significantly reduce the stresses concentration around the stope block. Thus, the formation of a stope chamber of a quasi-parabolic shape makes it possible to reduce vertical stresses as compared to horizontal ones without increasing horizontal pressure. When mining the extraction block, it is proposed to form the stope chamber of a quasi-parabolic shape with geometric parameters that directly depend on the parameters of the deposit, the depth of mining, and the direction of main stresses action. Dependences have been determined of the stresses value on the depth of mining and the physical properties of rocks, as well as on the length along the strike of the ore deposit. Thus, depending on the mining depth and length along the strike, rock pressure on the stope chamber of a quasi-parabolic shape decreases under non-uniform loading. The formation of a stope chamber of a quasi-parabolic shape will increase by 1.2 – 1.5 times the volume of pure ore that is recovered from the block.

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.

INVeSTIGATION INTO CROwN STABIlITy AT uNDeRGROuND leAChING Of uRANIuM OReS Purpose. Determination of influence of various factors on crown stability at underground block leaching of uranium ores. Methodology. Mathematical modeling applying the finite element and analytical methods is used to investigate into the impact of the ore body dip angle and crown workings on changes in the crown stress-strain state and stability. On this basis, dependencies of the above factors' influence on the crown stability are determined enabling their adequate consideration when specifying the appropriate crown thickness. Laboratory studies allow estimating influence of the reagent used at block leaching of uranium ores on their hardness for the purposes of determining safe crown parameters. findings. The dependencies of the ore body dip angle impact and the degree of crown disturbances caused by workings on crown stability as well as uranium ore hardness decrease resulted from application of the acid solution enable adjusting the appropriate crown thickness in determining safe parameters of the technology at the stage of the design work execution. Originality. Scientific novelty consists in determining dependencies that consider the impact of the ore body dip angle and the degree of crown disturbances caused by workings on crown stability. For the first time, influence of the sulfuric acid solution used in underground block leaching of uranium ores on changes in their hardness has been studied. Comprehensive consideration of the effect of these factors and the determined dependencies enables specifying safe thickness of crowns and ensures their integrity. Practical value. Possibility of adjusting crown thickness considering the ore body dip angle, the degree of disturbance caused by workings, and the acid solution impact will allow specifying the appropriate crown thickness at the stage of designing. This will allow avoiding possible failure of crowns caused by negative impacts of the above factors and ensuring safety of works.

The object of the study is a rock massif represented by complex-structured ore bodies mined by underground systems with open stoping or systems with bulk caving. Deposits of Kryvyi Rih iron ore basin are represented by different types of ferruginous quartzite, which enables application of a great number of mining systems to mining blocks. There are also barren rock inclusions within the block which are extracted from the block along with ore, and this reduces the iron content of the mined ore mass. Findings of the comprehensive study enable concluding that application of the selective method when mining a deposit can enhance recovery rates. Analysis of methods for determining rock stability results in ascertaining that in case of a 4–7 m thick inclusion of barren rocks it is advisable to use a system with bulk caving at a single stage, and in case of a 7–12 m thick inclusion – in two stages. The first stage involves mining the hanging wall reserves, the footwall reserves are mined at the second stage. This method is distinguished by leaving a barren rock inclusion in the block. The developed options of the mining system allow increasing the iron content in the mined ore mass by 2–4% and obtaining the expected economic effect from 3.0 M to 30.2 M USD depending on mining and geological conditions.

Purpose. Enhancing methods for determining parameters of drilling and blasting operations considering the stressstrain state of rocks. Methodology. Dependency of the inclined exposure dip on the stressstrain state of rocks to be caved is determined by the analytical research technique and mathematical modeling applying the finite element method. findings. The work offers methods for determining the energy intensity factor for breaking ores onto the inclined exposure which considers the exposure dip while correcting drilling and blasting parameters. There are also offered calculated numerical limits for the above factor. originality. The scientific novelty consists in determining numerical values of the energy intensity factor for break ing the rock massif considering its stressstrain state when caving onto an inclined exposure (compensation area) taking into account its dip. The work suggests limiting the range of obtained numerical values of the factor when breaking the massif onto any type of exposures. Practical value. Drilling and blasting parameters can be corrected depending on changes of the ore massif stress strain state when caving it onto any type of exposures (horizontal, vertical or inclined). The dedicated computer program created enables immediate acquisition of basic drilling and blasting parameters for particular conditions and analysis of predicted values of fragmentation of the massif to be caved.