Browsing by Author "Vasyliev, Leonid"

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    Comparison of the Reliability of Strength Limit Calculation Methods for Prismatic Samples with Different Spreading of Normal Contact Stresses in Their Wedge Failure Shape
    (IOP Publishing Ltd, 2024) Vasyliev, Leonid; Vasyliev, Dmytro; Malich, Mykola H.; Rizo, Zakhar; Kress, Denys
    ENG: This article explores methods for calculating the strength limits of solid objects subjected to compression. Traditionally, two stress distribution patterns are used: the exponential pattern by E.P. Unksov and the linear pattern by L. Prandtl. The authors introduce an enhanced stress distribution method. They compare the accuracy of these methods in calculating strength limits and constructing "normal stress - longitudinal strain" diagrams for wedge-shaped failures in rock samples. Four properties are considered: shear strength, coefficients of internal and external friction, and elasticity modulus. The results show that, with an external friction coefficient up to 0.3, all methods yield similar accuracy in strength limit calculations and ultimate stress-strain curves. Some curves exhibit stress drops, explained by a transition from convex to concave slip lines during failure. Additionally, there are hardening curves in the ultimate curves without theoretical justification. The comparison of calculated strength limits with experimental data confirms the method's accuracy: 13.7% error for the exponential method, 11.4% for the linear method, and 8.1% for the enhanced distribution, especially for low contact friction values (up to fc=0.3).
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    Fracture Diagrams of Prismatic Specimens with an Improved Contact Stress Distribution Law
    (IOP Publishing Ltd, 2022) Vasyliev, Leonid; Vasyliev, Dmytro; Malich, Mykola H.; Zhuravkov, Mikhail; Katan, Volodymyr
    ENG: The authors have previously improved the principles of distribution of contact normal and tangential stresses at the moment of destruction of the specimen on the basis of L. Prandtl's method as applied to rocks. The article presents further development of the method for constructing out-of-limit curves of "stress - longitudinal deformation" diagrams of rocks. A comparative assessment of the proposed method for calculating diagrams in comparison with diagrams has been constructed by E.P.Unksov method. It has been found that the parameters of the diagrams differ in numerical values in direction of increasing the reliability. Comparison of the calculated diagrams "stress - ordinate of the crack tip" and "stress - deformation" according to the improved method and the method of E.P. Unksov testifies that the level of the current strength values decreases with the development of two cracks at small angles of internal friction. The proposed method allows to determine the ultimate strength and residual strength of rock samples using their shear strength, internal, and contact friction coefficients, elastic modulus, which by simple methods can be established experimentally in laboratories of mining enterprises. The results can be used to control the state of the rock mass and effective destruction during disintegration.
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    Heading Set of Equipment for Underground Development Galleries Drivage in Rocks Prone to Gas-Dynamic Phenomena
    (IOP Publishing Ltd, 2022) Minieiev, Serhii; Vasyliev, Leonid; Trokhymets, Mykola; Maltseva, Vira; Vialushkin, Yehor; Moskalova, Tetiana
    ENG: The article presents the design of the heading set of equipment for drivage of development galleries in rocks prone to gas-dynamic phenomena. This equipment can carry out the full technological cycle of rock excavation. The use of the P-110 roadheader of Ukrainian PJSC "Novokramatorskyi Machine Building Plant" with an operating device on a telescopic boom is offered for the aggregation of the heading set of equipment for underground development galleries drivage in emission-hazardous rocks. The device for mechanized boreholes drilling in an emission-hazardous coal seam has been devised based on the EBGP-1 M drilling machine of the Ukrainian SPA "Chervonyi Metalist Co Ltd". This device is placed on the telescopic boom of the roadheader. For mechanized drilling of explosive, degassing, unloading and injection boreholes, a rock-breaking tool has been proposed that can perform an effective vibratory and rotary loading method of drilling in medium-hard and hard rocks. Safe methods for underground development galleries drivage in gas-bearing emissionhazardous rocks have been worked out. The effectiveness of these methods was determined in industrial conditions. It is possible to conclude that this new heading set of equipment and technology can be recommended for implementation in the mining coal industry.
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    Improving a Technique to Calculate Strength of Cylindrical Rock Samples in Terms of Uniaxial Compression
    (Dnipro University of Technology, Dnipro, Ukraine, 2023) Vasyliev, Leonid; Malich, Mykola G.; Vasyliev, Dmytro; Katan, Volodymyr; Rizo, Zahar
    ENG: Purpose is to improve analytical technique to calculate strength of cylindrical rock samples taking into consideration standard horizontal stresses. Methods. Mathematical modeling of cylindrical rock sample breakage under the truncated-wedge destruction was performed taking into consideration the standard horizontal stresses using four experimental characteristics (i.e. k being shear strength; fс and μ being contact and internal friction coefficients; and Е being elasticity modulus) as well as comparing the design strength with experimental data obtained in the process of uniaxial compression. Findings. The technique makes it possible to identify both maximum strength and residual strength of cylindrical rock samples using four indicators of properties which can be simply defined by experiment. Comparison of the analytical strength limits and experimental data, obtained in terms of uniaxial compression, supports the idea of high efficiency of the proposed technique. Originality. For the first time, analytical modeling of cylindrical rock sample breakage has been performed in terms of the truncated-wedge destruction taking into consideration the standard horizontal stresses as well as contact and internal friction parameters. Practical implications. The technique advantage is to apply promptly the calculation results in the context of industrial enterprises since their environment helps apply simple procedures to define indices of physiсomechanical characteristics of rocks for determination of stability of underground structures and reduction of energy consumption while disintegrating in open pits and mining and processing complexes.
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    Spall Fracture Forms of High Rock Samples under Uniaxial Compression
    (IOP Publishing Ltd, 2023) Vasyliev, Leonid; Bulich, Yurii; Vasyliev, Dmytro; Malich, Mykola G.; Rizo, Zakhar; Polishchuk, Alla; Kress, Denis; Kuttiubaev, Aidar
    ENG: Prof. L.I. Baron identified five forms of destruction during uniaxial compression of samples of regular geometry of rocks including truncated wedge, wedge, diagonal, longitudinal, and explosive forms. All of them are commonly characterized by the destruction of samples in their central parts showing two or more cracks, while the trajectories of crack development align with the corner points of the samples. Recently, was unexpectedly discovered a spall fracture in the form of a single crack emerged from the side wall of the specimen and propagating into it under uniaxial compression. Based on the discovery, the method for creating stress-strain diagrams for high rock samples was developed using four rock properties such as rock shear resistance limit, contact friction ratio, internal friction ratio, and modulus of elasticity. The stress-strain diagram of the spall fracture of high samples is described by a descending curve, which is typical for the diagrams of fracture created by two adjacent cracks of regular geometry samples. The maximum stresses required for the destruction of high rock samples are lower than those for the destruction of regular geometry samples of rocks with similar physical and mechanical properties.