Numerical experiments concerning long-term deformation of rock samples
A. Olovyannyy1, V. Chantsev2
1Saint-Petersburg Branch of the Federal State Budgetary Institution of Science of the Institute of Geoecology named after E.M. Sergeev of the Russian Academy of Sciences, Saint-Petersburg, Russian Federation
2Peter the Great Saint-Petersburg Polytechnic University, Saint-Petersburg, Russian Federation
Min. miner. depos. 2019, 13(4):18-27
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Purpose is to develop modeling methods of long-term rock sample deformation and failure under various loading conditions with the help of finite-element method of failure rock modeling (DESTROCK-FE).
Methods. DESTROCK-FE model describes rock as the non-linear viscoelastic-plastic breaking down medium. Creep strains are represented as viscoelastic ones, and viscoplastic strains are represented as the total of viscoelastic and failure strains. Destruction strains have been described by means of a model of the limited number of the oriented relaxation surfaces being calculated in accordance with shear and burst failure criteria. The calculations involved finite-element method for cylindrical samples. Numerical experiments have been carried out for following conditions: long-term creep under the permanent load; unloading strain after long-term creep strains; load relaxation in terms of the preset strain; and long-term strain in terms of gradual pressure increase. The research has involved rock-salt samples.
Findings. A model of rock as the non-linear viscoplastic failure medium has been added by a model of multi-defective medium. It has been determined that general nature of rock creep curves under permanent load, unloading, and stress relaxations, obtained by means of calculations, correspond to the available scientific notations. The fin-dings mean that the development of rock models should not involve successfully structural Maxwell element determining endless time-dependent strain growth. The strain velocity growth at the last stage of rock sample strain is stipulated by short-term and long-term accumulation of relaxations and failure.
Originality.It has been proved scientifically that viscous strains are described with the help of viscoelastic medium consisting of two Kelvin-Voigt elements as well as elements of short-term and long-term failure.
Practical implications. DESTROCK-FE modeling of one sample tested in terms of uniaxial compression has helped obtain parameters of elasticity, viscosity, and brittleness suitable for solving geomechanical and engineering problems in the context of mining.
Keywords: rocks, mathematical modeling, creep strains, stress relaxation, failure, finite-element method
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