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".

No abstract

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.

No abstract

The article studies stability of intervening pillars at underground selective mining of complex structured ore bodies of Kryvyi Rih iron ore basin applying open stope systems that will enable the increased useful mineral component content in the mined ore mass. When calculating an exposure span, the current methods of determining room system constructive elements do not consider dirt thickness. So, it is essential to develop methods of determining room system constructive elements for mining complex structured ore bodies to provide stability of stope exposures. When mining a mine block, stoping is suggested to be fulfilled gradually from the footwall to the hanging wall of the ore body by room-and-pillar methods leaving a dirt or ore inclusion in the block. This enables decrease in concentrating tension and compression stresses in the middle part of the dirt or ore inclusion resulting in its 1.5 – 2.0 times greater stability. There is also determined that the stope stability is impacted by the horizontal thickness of the inclusion, the hardness ratio and the order of stoping in a mine block. Application of open stope methods in selective mining of complex structured ore bodies of Kryvyi Rih iron ore basin enables increased quality of the mined ore mass without significant capital and operating costs and results in better environment of 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.

Криворізький національний університет ВИПУСК РУДИ З МАЛОРУХОМОЇ ЗОНИ НА ЛЕЖАЧОМУ БОЦІ ПОКЛАДУ ПОХИЛИМ ОЧИСНИМ ВИБОЄМ Мета. Метою роботи є аналіз, дослідження та розробка ефективних варіантів випуску відбитої руди біля лежачого боку рудних покладів з недостатніми кутами падіння при формуванні похилого обмежуючого контакту відбитої руди з очисним вибоєм. Методи дослідження. Виконано детальний техніко-економічний аналіз факторів і умов, які впливають на ефективність випуску відбитої руди з малорухомої зони біля лежачого боку покладів. Дослідження випуску відбитої руди виконувалось на лабораторних моделях з урахуванням масштабу моделювання. Застосування методів фізичного моделювання, заснованих на теорії подібності, дозволив зробити висновки, які лягли в основу наукових та практичних рекомендацій з випуску відбитої руди при формуванні похилого обмежуючого контакту відбитої руди з очисним вибоєм. Наукова новизна. Лабораторними дослідженнями встановлено оптимальні параметри пошарової відбійки руди, яка дозволяє здійснювати випуск відбитої руди з малорухомої зони на лежачому боці покладів з мінімальними втратами та розубоженням. Встановлено залежності товщини шару відбиваємої руди з урахуванням можливості отримання максимальних показників вилучення відбитої руди. Практична значимість. Виконаними дослідженнями розроблена та запропонована ефективна технологія пошарової відбійки та випуску відбитої руди, яка дозволить підвищити ефективність випуску без додаткових витрат на формування уловлюючих виробок лежачого боку та інших заходів, які застосовують на шахтах для вилучення запасів малорухомої зони на лежачому боці покладів. Результати. На підставі виконаних досліджень та встановлених залежностей запропоновані оптимальні варіанти технології пошарової відбійки та випуску відбитої руди при формуванні похилого обмежуючого контакту відбитої руди з очисним вибоєм. Доведена доцільність відбійки похилими шарами з формуванням обмежуючого контакту відбитої руди з очисним вибоєм. Запропоновано пошаровий випуск похилим потоком. Ключові слова: лабораторні дослідження, руда, похилий забій, пошарова відбійка, пошаровий випуск, лежачий бік, втрати.