O. M. Usol’tseva

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 state and properties of various-scale geomechanical objects using solutions of inverse problems

The authors comment on features of formulation and structure of input data for the inverse problems used in rock mechanics to estimate state and properties of natural and anthropogenic objects at various spatial scales. The article gives examples of using solutions of inverse problems in coal bed degassing monitoring, based on data on changes of pressure in hydraulic props in the overlying bed, and in assessment of deformation parameters of inclusions, based on data of uniaxial compression tests of artificial heterogeneous specimens.

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.

Experimental investigation of plastic pure-shear deformation under simple and complex loadings

ConclusionsThe inelastic properties of solid bodies under simple and complex loadings that result in pure-shear strain and successive superposition of deformed states of pure shear are investigated experimentally. The strain anisotropy that develops in this case is satisfactorily described by the hypothesis of anisotropic hardening, which must be considered in constructing constitutive relationships of the theory of plasticity of rocks.For these types of loads, there are uniqueσi(ɛi) andσ1(ɛ1) cuves that can be used as rating curves for the material in calculations.These effects may be used as a production procedure for controlling the anisotropy of the metal in tubular structural components in mining-machine building and the creation of prescribed (improved) strength properties in these components.

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.