Browsing by Author "Malich, Mykola H."

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    Analytical Method for Calculation of the Strength of Cylindrical Rock Specimens during Their Longitudinal Stress
    (M.S. Poliakov Institute of Geotechnical Mechanics of the National Academy of Sciences of Ukraine, Dnipro, 2023) Vasyliev, L. M.; Vasyliev, D. L.; Malich, Mykola H.; Katan, V. A.; Rizo, Z. N.
    ENG: The goal of this research is to develop a method for calculating the strength of cylindrical rock specimens under axial failure. This will allow for the management of the stress-strain state of rock masses, which is an important issue for many mining companies. To achieve this goal, analytical modeling of the process of failure of cylindrical rock specimens under axial failure was carried out. This was done using experimental values of four indicators of rock properties: shear strength, coefficients of internal and external friction, and elasticity modulus. The results of this research allow for the determination of the ultimate strength and residual strength of cylindrical rock specimens using the four property indicators. These indicators can be experimentally determined using simple methods in laboratory conditions of mining companies. The scientific novelty of this research lies in the fact that analytical modeling of the process of failure of cylindrical rock specimens under axial failure was conducted for the first time, taking into account internal and external friction. This allowed for new results to be obtained and provided a basis for the development of new methods for managing the state of rock masses. The practical significance of this research lies in the fact that the proposed method allows for the determination of the ultimate and residual strength of rock specimens using four property indicators. These indicators can be experimentally determined in mining company laboratories, making the calculation results applicable for the management of the state of rock masses and the efficient destruction of rocks during disintegration. Thus, this method has significant practical significance for the mining industry. A method for calculating the strength of cylindrical specimens under longitudinal failure mode has been developed. The average convergence of calculated strength values with fс = 0.5 to experimental data is 83.4%, which corresponds to a good level of reliability for rock materials. It has been shown that the self-organization of longitudinal failure mode in cylindrical rock specimens occurs in accordance with Coulomb's criterion of maximum effective shear stress, which has been improved to account for contact friction.
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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.