Purpose. Development of an analytical method for calculating the parameters of complete diagrams longitudinal tension deformation for the truncated-wedge shape of destruction of cylindrical rock samples to control the stress-strain state of the rock mass and effective destruction of these materials during disintegration. Methodology. Analytically, by developing a mathematical model of the fracture process of cylindrical rock samples with their truncated-wedge form of crack development, an algorithm is created for calculating the full deformation diagram from the acting tension using the experimental values of four indicators of material properties the shear resistance limit, internal and external friction coefficients and elastic modulus. The method is based on the improved Coulomb strength criterion, supplemented by the parameters of contact friction and allowing one, using the theory of slip lines, to calculate the limiting state of the material at the tip of cracks developing from the edges of the sample of the correct geometry, taking into account the release of part of the material from the load and compliance with Hookes law deformation of the sample bearing area and the specific force on it. Findings. The method of mathematical modeling makes it possible to determine the ultimate strength and residual strength of cylindrical rock samples using four property indicators that can be experimentally established by simple methods. Originality. For the first time, analytical modeling of the process of destruction of cylindrical rock samples with their truncated-wedge form of destruction was carried out, taking into account the internal contact friction depending on the properties of the rock material and external contact friction. Practical value. The proposed method of mathematical modeling and the calculation algorithm make it possible to determine the limit and residual strength of rock samples using four property indicators, which can be established experimentally by simple methods under laboratory conditions of enterprises of the mining and metallurgical complex. The calculation results can be quickly used to control the state of the rock mass and effective destruction upon disintegration.
The purpose of this study is investigation of the patterns of occurrence of the system of macro and microcracks in the rocks during rapid cooling for their effective softening.Methodology. The solution of the problem of crack system development is based on the fact that, as a result of rapid cooling in the surface layer of the rock, the tensile stresses are developed. The stretched layer acquires potential energy, depending on the modes of thermal influence and rock properties. At a certain point, the energy of the stretched layer starts to be spent on the forma tion of new surfaces of the growing system of macro and microcracks.findings. A model of behavior of the surface layer of rocks in the conditions of thermal shock by cooling is proposed. This model takes into account the development of a fracture macrocrack system and a microcrack system that move in the layer behind the cooling front. The dependence has been obtained that allows determining the penetration depth of a macrocrack system in the rock depending on the thermal exposure regimes and the physical and mechanical properties of the rocks. The formation of a microcrack system in the stretched cooled surface layer which changes its strength properties is experimentally proved. It is shown that the system of macrocracks moves into the array with deceleration and penetrates into the rock deeper than the thickness of the cooled layer, while microcracks are formed within the extended cooled layer. It is shown that the penetration depth of the macro crack system into the rock is practically independent of the mode of thermal shock by cooling and is determined by the physical and mechanical properties of the rock and the time of exposure. Increasing the potential energy of the stretched rock layer due to an increase in the temperature difference between heating and cooling ("toughening" of the thermal shock regime) leads mainly to an increase in the density of a cracking net on the rock surface. originality. For the first time the development of a crack system rather than a single crack in a rock during rapid cooling was considered. The model of the rock surface layer behavior under the conditions of rapid cooling is proposed. The geometric aspects of the initiation and propagation of a macrocrack system into the rock due to thermocycling loading are considered. The fact of initiation of a microcrack system along with macrocracks which change the strength properties of rock in the formation zone is proved.Practical value. The analytical dependence is obtained that allows determining the penetration depth of a crack system in rocks as a result of thermal shock by cooling. This dependence makes it possible to estimate the size of the damaged by macro and mi crocracks zone of a rock, as well as the degree of rock softening depending on its physical and mechanical properties and thermal shock modes of cooling. The results are used in real technological processes with thermocycling impact such as preparing rocks for mechanical destruction, hydraulic fracturing, ...
Elevated bearing load pressure is formed near the exposed part of the coal seam, compared with static stresses normal to the reservoir. The loading of the near-bottom part of the coal seam is formed by linearly damped, according to the principle of Saint-Venant, from the bottom of the face to the massif of the tangential stresses from contact friction between the formation and lateral enclosing rocks in the form of a reference rock pressure, the epure of which is described by a convex quadratic function whose initial value is normal stress at the top of the bottom hole fracture, and the final stress is to the rock pressure in the zone of the intact massif. In connection with the above scientific position, a method has been developed for determining the vertical normal stress at the top of the bottom hole fracture, the length of the epure, and the distance from the bottom to the maximum of the reference pressure.
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