P. A. Tsoi

Evolution of stress-strain state in structured rock specimens under uniaxial loading

The comprehensive experimental studies into the change in the stress-strain state of rock specimens subjected to uniaxial loading until failure, using the automated digital speckle photography analysis shows that when the stress reaches 50% of the limit strength of the specimens, low-frequency micro-deformation processes begin in the specimens under slow (quasi-static) stiff loading. The amplitude of the deformation-wave processes depends on the level of the pre-set macro-loading. Wave packets are plotted for averaged microstrains obtained in sandstone and marble specimens under uniaxial compression. Fourier transforms are used to define the amplitude-frequency characteristics of four micro-deformation stages: elastic, nonlinearly elastic, post-peak and residual strength stages. Elastic oscillations with frequency 0.5–4 Hz appear at the pre-failure stage and continue at the post-peak loading stage.

Genesis and evolution of discontinuities in geomaterials: Theory and a laboratory experiment

The authors designed and manufactured a test stand to study origination and evolution of discontinuities in rocks. Based on the laboratory experimental data obtained for artificial geomaterials and the new-developed geomechanical model, the state equation for shear deformation of a discontinuity is synthesized.

Nonlinear deformation–wave processes in various rank coal specimens loaded to failure under varied temperature

Aiming to build up a phenomenological basis for the theory of interaction between geomechanical, thermal and physicochemical processes in methane-bearing coal in Kuzbass, the authors performed a set of laboratory bench tests on uniaxial stiff loading of various rank coal specimens. The pressure versus temperature dependences are obtained for coal specimens with granite gaskets using high-precision scanning computerized thermal imager. It is shown that temperature changed in coal specimens subjected to loading to failure is connected with volatile content and internal energy relaxation of methane in Kuzbass coal. Using jointly thermal imaging and laser measuring equipment ALMEC-tv for high-precision and detail control of deformation–wave processes in loaded coal specimens by speckle-method, it has for the first time been proved that nonlinear pendulum-type movements of structural elements are possible in coal specimens with varied temperature field, which is of fundamental importance for actualization of previously ignored mass and gas exchange processes in high-stress coal beds of different grade composition under mining,

Measuring equipment and test bench to control evolution of acoustic-deformation and heat fields induced in solids under failure by fluids

The authors have developed a procedure and a test bench for studying evolution of various nature physical fields in modeling geomedium fracture by fluids. The test bench performs synchronous recording of macro- and micro-deformation, heat and acoustic emission induced in physical models of geomedium under loading to discontinuity. The experimental procedure has been trialed. The analysis of the synchronized test data allows a conclusion on the existence of time–space relationship between different nature physical fields induced during failure of solids.

Estimation of strength properties of rock samples in terms of calculated Mohr’s envelopes

The paper presents the theoretical determination method for rock strength properties under uniaxial and triaxial compression. The experimental values of ultimate strengths of dolomite and granite samples are used as the initial data. The correlation between the calculated and experimental data has been stated.

Investigation of Strength of Anisotropic Rocks under Axial Compression and Lateral Pressure

The article describes the theoretical and experimental research into the strength of cylindrical specimens made of layered and anisotropic geomaterials exposed to axial compression and lateral pressure. The tests used INSTRON 8802 versatile servohydraulic fatigue testing system. The experimental results are the relationships between the ultimate strength and bedding angle in specimens of an artificial material, meta-siltstone and shale. The experimental data agree well with the theoretical calculations.

Modeling evolution of damage in rock specimens under loading

Based on the integrated analysis of micro-strains obtained using white light specklephotography method in Brazilian Test of rock specimens and analytically calculated elastic fields of stresses and strains, the authors show that there exist significant correlation dependences between the damage in a certain domain of a rock specimen and the level of the external load. Given a verified geomechanical model describing properly evolution of stresses in a rock specimen, this fact offers pre-requisites for estimation of damage in different areas of a rock specimen by monitoring condition only in one of such areas.