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.

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.