The authors compare the strength characteristics of rocks, determined by standards GOST 21153.8-88 and ASTM D7012-04. The research involved 7 rock lithotypes (shale, diabase, metasomatic rock, marble, gneiss, quartzite, garnet) and bulk compression, uniaxial compression and indirect tension testing. Mohr’s circles and failure envelopes are plotted for each rock lithotype. The differences between the standards are found in terms of adhesion factors and internal friction angles: ASTM yields higher adhesion factors; internal friction angles vary depending on the rock type. The calculation formula allows predicting the uniaxial compressive strength at an error of 10.5

The authors investigate geophysical parameters of water-saturated and frozen rock samples, and compare the results with the data of natural rocks. The samples were subjected to dynamic loading, an acceleration signal was recorded and a spectral density was calculated. On this basis, later on, the authors determined the longitudinal vibration velocity, the logarithmic decrement of damping, the internal friction factor and the acoustic Q-factor. The water-saturated and frozen rock samples demonstrated the increased velocities of longitudinal vibrations. The samples, which had the high acoustic Q-factors in the frozen conditions, fractured under much higher loads. The degree of water saturation affected the strength of the test samples: their strength reduced with the higher water saturation. Freezing of the samples generated microseismic vibrations in the region of high frequencies. In the uniaxial compression tests to failure of the samples under critical loading, a high frequency signal was recorded during initiation of an extension fracture, and the signal spectrum shifted toward lower frequencies as the fracture grew.

Исследованы физико-механические свойства роговика, габбро-долерита и богатой халькопирит-пирротиновой руды Октябрьского месторождения Талнахского рудного узла, подвергшихся затоплению. Анализ петрографии, элементного и минералогического состава образцов показал, что существенных различий в их свойствах после затопления не наблюдается. Сравнение деформационно-прочностных характеристик при испытаниях горных пород и руды на одноосное сжатие и растяжение демонстрирует их уменьшение в водонасыщенном и увеличение в высушенном состоянии при комнатной температуре. Пределы прочности, модули упругости, сцепления и углы внутреннего трения имеют меньшие значения после высушивания, чем в исходном состоянии. The authors investigate the physical and mechanical properties of hornstone, gabbro-dolerite and rich chalcopyrite-pyrrhotine ore subjected to flooding at the Oktyabrsky deposit in the Talnakh ore province. The analysis of the petrography, chemistry and mineralogy of the test samples showed no substantial differences in their properties after flooding. The comparison of the strength and deformation characteristics of rocks from the uniaxial compression and tension testing results demonstrate the decrease of both in water-saturated rocks and the increase in the room-temperature dried samples. The limit strength, elasticity modulus and internal friction angles have smaller values in rocks after drying than in the initial samples.

The authors investigate the physical and mechanical properties of hornstone, gabbro-dolerite and rich chalcopyrite–pyrrhotine ore subjected to flooding at the Oktyabrsky deposit in the Talnakh ore province. The analysis of the petrography, chemistry and mineralogy of the test samples showed no substantial differences in their properties after flooding. The comparison of the strength and deformation characteristics of rocks from the uniaxial compression and tension testing results demonstrate the decrease of both in water-saturated rocks and the increase in the room-temperature dried samples. The limit strength, elasticity modulus and internal friction angles have smaller values in rocks after drying than in the initial samples.

This work is devoted to the experimental study of the combined effect of temperature and water saturation of rocks on their impact hazard properties. The host rocks of the “Zarnitsa” kimberlite pipe of the Republic of Sakha (Yakutia)—limestone, marl, dolomite, sandstone and siltstone were tested in laboratory experiments at the temperature from +20 to –60°C and different degrees of water absorption: air-dry state, partially water absorption state and fully water-saturated state. Analysis of the values of ratio of the modulus of decline M and deformation E showed that rocks having high water saturation degree acquire hazardous properties in water-saturated state at low temperatures, although they do not exhibit such properties at the temperature of +20°C.

The experimental study was carried out and patterns of changes of the strength properties of rocks were obtained under uniaxial compression and shear with compression loading of host rocks (limestone, marl, dolomite, sandstone and siltstone) of “Zarnitsa” kimberlite pipe (Mirny region of the Sakha Republic, Yakutia) of different degree of water saturation in the temperature range from +20 to –60°C. For the studied rocks, empirical dependences are constructed of the uniaxial compressive strength, ultimate shear strength, cohesion, and internal friction angle on the temperature and the degree of water saturation of rocks. The analysis is carried out of strength properties of rocks and the conclusion is given about the combination of the most dangerous factors leading to the destruction of the rock.

The nature of changes of the parameters of microseismic emission signals (MSE) contains important information about the stage of the deformation process during the destruction of rocks under various types of loading, and can also give predictive estimates of the destruction of the massif. In this paper, the study of the MSE behavior is carried out signals under direct shear loading of samples from tuff sandstone, siltstone and clay crust weathering. The analysis of changes of the parameters of the MSE signals: the number, amplitude of acceleration and frequency at the pre-limit stage, the limit load and the post-peak stage of deformation is given.

An experimental study is carried out of the deformation process of the samples of siltstone and limestone with joints under direct shear with constant compressive load. The values of the degree of water saturation and the roughness coefficient of surfaces of joints varied. The aim of the work was to study the character of changes of the parameters of microseismic emission signals depending on the degree of water saturation and the roughness coefficient of the samples under direct shear loading. The first signals of microseismic emission appear at the stresses of 0.3–0.4 of the shear strength for the siltstone samples with high surface roughness values. The number of signals increases at the maximum load value and remains significant until the residual strength section. The highest values of the acceleration amplitude correspond to the break-downing of high roughness peaks. The direct shift occurs during monotonous sliding without sharply pronounced damage for limestone samples that are in a completely water-saturated state. It is confirmed by the absence of significant changes of the characteristics of microseismic emission signals.

This paper presents the results of the experimental study of the influence of sizes effect on the strength and deformation characteristics of samples of hornfels, limestone, sandstone, siltstone and ore-bearing rocks. Tests were performed on cylindrical samples of three sizes of diameters - 10, 30 and 60 mm under uniaxial compression and tension loading. The results of the study demonstrated that the values of ultimate strength decrease when the size of samples increases for the samples of cornea, limestone, sandstone and siltstone. The ultimate strength increases with increasing of sample size for ore-bearing rocks containing viscous inclusions. The samples of smaller size of ore-bearing rocks exhibit a brittle character of the fracture for all types of rocks, and the viscosity of fracture increases with increasing size of samples. the obtained regularities were analysed from the positions of otwo types of size effect (volume and surface).

The rational mine support system designs for underground excavations in backfill are discussed. The current mine support technology applied in excavations in backfill in Artemievsk and Orlovsky mines is examined. The strength and deformation characteristics of backfill samples are tested on a laboratory scale. The FEM-based stress–strain analysis of ore body and backfill is described with the assessment of their stability. The probable failure zones in backfill and ore body during to-downward slice mining are determined. The rational support design is validated for backfill having stability category I, II and III. The pilot test data on the load-bearing capacity of friction-anchored rock bolts in backfill are assessed. The economic efficiency of the mixed-type support composed of steel frame and friction-anchored rock bolts in backfill is demonstrated.

Shear destruction of rock mass along weakened planes is one of the main reasons of the failure of career boards, underground workings and rock slopes. The paper deals with laboratory testing of rock joints under direct shear loading. Special test and measurement complex was created to study deformation and strength characteristics of rock joints. Test specimens were made from single slab of sandstone of homogeneous structure. Shear tests have been conducted under constant normal load (CNL) and constant normal stiffness (CNS) boundary conditions at three values of normal compressive stress: 0.5 MPa, 1.2 MPa and 1.8 MPa. The analysis of test results allowed to reveal patterns of changes of deformation-strength properties of rock joints depending on the level of normal load, boundary conditions and roughness values. The ultimate shear stress is always higher under CNS boundary condition than CNL for the same values of normal compressive stress. Shear stress practically retains constant value after reaching the ultimate stress under CNL boundary conditions and it decreases under CNS conditions. The values of ultimate shear stresses, shear modulus and the length of linear section on “shear stress–shear displacement” curve increases with increasing surface roughness at the equal levels of normal compressive stress.

The research was performed of strength properties and failure mechanism of shale samples of layered structure under shear loading with coupled compression. The effect of angles of orientations of stratification planes Ψ and angles of shear plane Δ on ultimate shear strength of shale specimens was analyzed. The results indicate that ultimate shear strength depends on combination of values of bedding angle and angle of shear plane relative to the stratification. The empirical dependences of the cohesion on angles Ψ and Δ were obtained. Minimum and maximum values of cohesion have been defined depending on values of angles Ψ and Δ. The combinations of angles Ψ and Δ are determined that are most dangerous for shear fracture of rocks of layered structure.

Indices of strength properties are a mandatory indicators characterizing the mechanical behavior of rocks in the process of conducting civil and industrial geoengineering work. To assess the strength properties of rocks, both in-situ and laboratory test methods can be used, which have their pros and cons. The first are considered reliable and time consuming, the second - less time consuming and less reliable. The definition of the correlation dependences between the indices of strength properties was carried out by researchers all over the world, in particular, by outstanding Russian mining scientist Protodyakonov M. M. In this paper, some of its dependencies were analyzed and refined: compressive strength versus tensile strength, compressive strength versus shear strength, shear strength versus tensile strength, shear strength versus cohesion coefficient.

The research was performed of influence of dynamic pulse effect on mechanical behavior of geomodels with discontinuities that are under constant static shear load. The values of vertical impact energy, the values of horizontal static load, and the values of the roughness of the discontinuity surfaces were varied. It is concluded that dynamic impact leads to a shear of lower part of the geomodel relative to upper one in the horizontal direction at loads less than the shear strength of this model when exposed only to static load. The shear displacement increases with increasing vertical impact energy almost linearly. The amplitude of microseismic emission signals increases and the number of signals decreases with increasing roughness of the discontinuity surfaces.

The present work is devoted to revealing the regression dependence of the discontinuity profile length (L) on the joint roughness coefficient (JRC). Involving the profile scale data of Barton-Choubey and subsequent statistical analysis, a forward and inverse regression relationships between the values of JRC and L are obtained in the form of the third degree polynomial functions. Using the 3D scans of rock sample joints (obtained from the Brazilian test) and inverse regression relationship "L versus JRC", the variability of the joint roughness coefficient over the entire cleaved surface is shown. For a generalized roughness assessment, it is proposed to use the mean value of the joint roughness coefficient.

The authors discuss the problem connected with insulation of exposed rock surface areas against the aggressive influence of mine atmosphere and rock falls during mining. The lab-scale tests determine the moisture effect on the strength of rocks in the Orlov Ore Field. The tensile strength of samples of isolation membrane as well as their adhesion to rocks and shotcrete is assessed. The technology of preparation and application of polymer membrane insulation layer on the surface of differently damaged areas on the roof and sidewalls in stopes is justified for the Orlov Mine.

Проведены испытания на образцах с нарушениями сплошности из искусственного геоматериала (бетонно-песчаной смеси) с треугольным профилем шероховатости поверхностей при трех значениях нормальной сжимающей нагрузки: 0.5, 0.9, 1.2 МПа и сдвиговом нагружении с граничным условием "постоянная нормальная жесткость".Определены закономерности деформирования на каждой стадии диаграмм нагружения: линейной, нелинейной, при пиковой нагрузке и стадии остаточной прочности.

Determining the elasticity modulus of rocks for uniaxial tension is technologically challenging, therefore, at the present time some indirect methods for estimating such a mechanical parameter exist. In this work, it was estimated the elasticity modulus for uniaxial tension using data from the Brazilian test with post-registration of strains using a virtual extensometer (digital image correlation).