Home – Home – Jornals – Fundamental and applied issues of mining 2021 number 1

The problem of hydraulic fracture development near a circular cavity is considered in a three-dimensional homogeneous elastic medium. The results of numerical calculations using the extended finite element method (XFEM) implemented in the ABAQUS software package are presented. Different variants of the position of an initial disk fracture relative to the cavity are considered. Some patterns of a 3D hydraulic fracture development near the cavity are found.

According to the borehole logging analysis and near-field transient electromagnetic sounding method, a positive electric resistivity anomaly was detected from top to bottom along the section above the abandoned coal seam. This anomaly indicates a downward movement of groundwater and saturation of rocks with gas.

To study the stress state of “soil body with an inclined earth surface - a system of parallel tunnels” objects, an analytical calculation method is used, which is developed on the basis of obtained new solution to corresponding elasticity theory problem. This method is implemented as a computer program that allows numerical modeling in practical design. Examples of calculation are given.

This article proposes a method based on the disruption theory of an arbitrary discontinuity (the Riemann problem) to determine the shock wave parameters on the wall of an explosion cavity. Two possible variants of detonation wave refraction on the explosion cavity wall are described. The detonative decomposition of emulsion explosives is also considered, and an equation of state for gaseous explosion products is proposed, which enables the estimation of detonation parameters while accounting for the incompressible volume of molecules.

The approaches to the creation of databases that accumulate various information about the deposits of solid minerals are considered. The structure of the database of rocks of the Elginskoe coal deposit and the procedure for filling with information of its constituent sections are proposed. It is shown that the database use provides the highest level of information and analytical support of the geotechnological problems focused on the safe mining and completeness of reserves extraction from the subsoil. A number of coalfield models have been built using specialized software based on the database. The stability analysis of overburden massif of the coalfield has been carried out and geomechanical conditions of open-pit sides have been evaluated.

The problem of constructing a continuous model of hierarchical block geomedium is considered. The basic structural element providing the geomedium structuring is determined, and transition from a hierarchical block to a hierarchical structured medium is discussed. The introduction of four structural levels is sufficient for modeling the geomedium within the Earth’s crust. To describe the fractured structures, a non-Euclidean model of the continuous medium is applied, which considers the violation of deformation compatibility conditions. An algorithm for the transition to a continual description of such structures is presented and nonsingular solutions for a plane-stressed field are constructed. The performed analysis showed that this approach requires hierarchical non-Euclidicity and monolithic block principles.

A method estimating the stress state of anisotropic rock mass around an excavation of an arbitrary cross section is proposed. The technique is based on a new solution of the plane problem of anisotropic elasticity theory obtained using Lekhnitsky complex potentials. For a number of anisotropic rocks, the dependences of maximum compressive and tensile stresses in rock mass around the arched excavation on the inclination angle of an isotropic plane have been found. Comparison of stress distribution around excavations driven in isotropic and anisotropic rock masses is performed.

The authors discuss the structure and formation character of technogenically changed subsoil. A quantitative assessment of the stability of technogenically changed rock mass is proposed, obtained as the sum of the indicators determined using various geophysical and geomechanical methods and characterizing the array of indicators converted into dimensionless quantities by the ratio of their values changed during mining operations to the initial values.

Comparison of Brazilian tensile strength with uniaxial tensile strength is presented. It is noted that on the basis of only statistical processing, it is possible to obtain only rough estimates of direct tensile strength from the measured Brazilian strength. To agree on these values, models that take into account the structure of the material should be used. Taking into account the biaxiality of the stress field, which leads to a decrease in Brazilian strength compared to direct tensile stretch, and considering the nonuniformity of tensile stresses causing the opposite effect, it is possible to correlate the values of tensile strength measured by different methods.

The necessity of expanding the possibilities for controlling the explosive action to obtain a uniform rational fragmentation of the run-of-mine with a minimum yield of oversized and fine low-grade fractions is substantiated. The methodological problems of applying the smoothed particle method for 3D modeling and studying the patterns of dynamic loading of a rock mass, the uniformity and intensity of crushing in different explosive zones, as well as problems of two- and three-dimensional model calibration are considered. The method is calibrated by simulating the fragmentation process by an explosion in comparison with experimental results on blasting rock samples during the explosion of an elongated borehole charge. Work was carried out to study the influence of drilling and blasting parameters and kinetics of energy release on the intensity and uniformity of fragmentation. The regularities of the effect produced by specific consumption of industrial explosives, the rate of energy release; the distance between boreholes, the diameter of borehole charges, as well as air gap values on the intensity and uniformity of crushing in different explosive zones are determined.

The results of numerical modeling of rheological processes both in the potash rock mass in the vicinity of an underground loading complex and in the lining of an underground structure are presented. An algorithm is proposed for solving the problems of calculating the durability of large-scale underground structures with an insufficient amount of initial data on the rheological properties of lining materials for underground structures and the enclosing rock mass. It is shown that even in such conditions, it is possible to qualitatively assess their geomechanical state in the long term. Comparison of various approaches to modeling rheological processes is made.

The problem on elastoplastic deformation and failure of rocks around cylindrical and spherical cavities under the action of internal and external pressure is considered. The pressure during hydraulic fracturing is customary determined by the theory of maximum normal stress. However, the known laboratory experimental studies are not confirmed by this theory. For this reason, it is proposed to determine the limiting pressure using different experimentally justified failure criteria.

The results of calculating the stability of a slope on which the dump is planned to be placed are presented. Safe direction of dumping on the slope is determined, which ensures the slope stability during mining mountaintop deposits of Kyrgyzstan.

The influence of block structure of the rock mass on the stability of sides of mountaintop quarries is estimated. The results of laboratory studies of deformation and destruction along the contacts of blocks, depending on the composition of filler between the blocks, are presented. It is found that shear resistance along the contacts of blocks depends on the composition and internal friction angle of the filler.

The formulation of the problem and results of studying the stress state of the support and rock mass around the excavation in rocks with low values of the fracture strength are presented. The features of performing geomechanical calculations in inhomogeneous continuous medium with significantly different mechanical properties and geometric dimensions are discussed. The nature of support deformation when filling the voids formed during the rock destruction in the roof and sides of the excavation with foaming phenolic resins is determined .

Based on the results of long-term researches in construction and subsequent operation of a railway tunnel using the automated monitoring system, the formation pattern of the stress-strain state of permanent lining made from cast reinforced concrete was obtained. It is found that vibrodynamic loads from transport to the tunnel foundation affect the exclusion of temporary unclosed support from the work with surrounding rock mass .

Studying of rock mass deformation with weak zones is based on the principal property of applied nature that limits incorrectness: the influence of an underground excavation on the stresses and displacements in rock mass attenuates to zero as the distance increases - this is a postulate. The author suggests reducing the problem to solving an additional problem on tensile stresses at the underground excavation boundary to ensure uniqueness and correctness of the elastic solution.

The mechanism of blasting destruction of coal is considered using a combined model of gas-saturated coal, which describes the relationship between explosive damage of a coal seam and subsequent gas release. On the basis of this model, the numerical method of smoothed particles is used to study the development of destruction zones and stress-strain state of a coal seam in the vicinity of a borehole charge after blasting. The obtained patterns help to predict the reaction of coal to explosive dynamic impact. This may be of considerable interest for the development of technology for preliminary degassing of coal seams, as well as for theoretical description of the processes occurring during coal and gas emissions. In this regard, the preparation mechanism of gas-dynamic fracture of a stack of outburst-hazardous (broken) coal under explosive action on a coal seam is considered. The research includes studying the conditions for crack formation in the zone farthest from the blast hole, modeling the filling of induced cracks with methane, which is initially in the coal in a dissolved state, and estimating the onset time of induced crack propagation due to free methane pressure in the crack. It was found that, depending on the mechanical and diffusion parameters of coal, the crack initiation time can vary from tens of seconds to many hours. The research results can be useful in the development of a theory of explosive action on a coal seam, which is used in a set of measures to reduce the hazard of sudden coal and gas emissions.

The physical and mechanical properties of soil from the place of landsliding are studied in laboratory conditions. The problem is solved under the assumption that the landslide mass before and after landsliding remains unchanged. The value of the landslide mass is determined. By constructing various possible sliding surfaces and determining stability factor for each of them, the most dangerous sliding surface was found. To ensure the safety of residential settlements and other objects located at the base of landslide slopes, it is necessary to know the distance that the landslide will travel when fully unloaded. The distance of displacement of landslide masses in the horizontal section is determined.

The density ratio is normalized with respect to the theoretical maximum density ratio of a sphere packing, which is 0.7405. The experimental data show that the density ratio of a packing of sized glass balls changes during cyclical shearing .

An analytical method is presented for determining the stress state of a rock mass in the vicinity of a circular opening, taking into account the influence of contact anchors with high rigidity. The method is based on the solution of a plane problem from the elasticity theory about the equilibrium of a weighty isotropic medium with a circular hole, around which there is a certain region reinforced with an arbitrary number of radially installed rods with high rigidity. The calculation examples illustrating the possibilities of the method are presented. For the purpose of comparison, the corresponding results of computer modeling using the finite element method are considered.

The problems of calculating the stress-strain state of an ore body, enclosing and backfilling masses during the development of mining operations at deep horizons are considered. The previously developed algorithm for taking into account the sequence of stoping and backfilling operations to redistribute the stress fields in rocks for modeling the nonlinear properties of backfilling material has been modernized. The calculation is carried out by the method of conic elements using the stiffness matrix formed for an intact rock mass. The nonlinear behavior of backfilling material is taken into account using the initial stress procedure that is also used to model the sequence of sinking and backfilling of stopes.

The results of mathematical modeling of permafrost rock mass deformation around a mine working with circular cross-section are presented and the influence of thawing on stress state of the rock mass and mine working stability in conditions of a hydrostatic stress field is studied. It is shown that there is a critical size of the thawing halo, upon exceeding which the working starts loosing stability .

The issues concerning the influence of temperature factor on safety and efficiency during the underground mining of mineral deposits in the areas with permafrost rocks are set forth. The features of mining operations and the formation of a thermal regime in alluvial mines of the permafrost zone have been determined. It is shown that the main requirement for regulating the thermal regime of a mine is to prevent thawing of dispersed rocks surrounding mine workings. The results of predictive calculations (by the method of mathematical modeling) of the temperature regime in air supply workings, as well as in enclosing rock mass of a designed alluvial mine, are presented. The results of mathematical modeling of the temperature regime of soils in the area of pile foundation of a tower-type drop hammer and the mouth of a vertical shaft are considered. Based on the results of numerical modeling, recommendations are given to organize automated control of soil temperature (horizontal wells) of the wellhead.

The parameters of physical, mechanical, rheological and water properties of clay rock in the Kara-Keche coal quarry are presented. It is found that in relation to water, gray clay is a swelling-proof and impervious rock. Its presence at the boundary of slip line surface contributes to the activation of landslide phenomena in the open-pit sides. It is determined that gray clay has a pronounced rheological ability to develop plastic flow deformations. The dependence of effective viscosity of gray clay on humidity value was revealed. It is shown that theoretical and experimental values of effective viscosity are in good agreement.

The behavior of cohesion coefficients and internal friction angles depending on the linear or nonlinear representation of the Mohr envelope as a functional dependence of the shear stress on the normal stress is studied. The calculations were based on the reference data concerning ultimate compressive and tensile strength of rocks. The linear dependence was constructed as a tangent drawn to two Mohr circles, and nonlinear dependence - as a relationship recommended by the domestic standard.

The problem of penetrating a weighty rock mass with the Coulomb-Mohr plasticity condition with a rigid nondeformable wedge-shaped tool is being solved. In this case, the relations on the characteristics, as a consequence of differential equilibrium equations, are obtained by the terms that identify them with ordinary linear differential equations of the first order. As a result of equation integration, the required values of contact stresses at the “tool-rock” interface are determined. The ultimate load depends both on the angle of tool sharpening and physical/mechanical rock characteristics, and the depth of penetration.

In the axisymmetric case of Leibenson - Ishlinsky formulation, the problem of stability loss in a mine working with initial circular cylindrical shape is solved. It is assumed that at the moment of stability loss bulges are formed, facing the inside of the mined-out space. The rock mass around the mine working is considered in one of three states: elastic, elastoplastic and post-limiting deformation. The critical load depending on the length of working, radius and physical/mechanical rock properties is determined.

It is shown that inhomogeneity of the structure and variability of the rock mass properties has a great influence on the mining efficiency of complex deposits, which include the section Uregolsky of the open pit mine Kiyzassky. Field observations were carried out to assess the state of the rock mass on the overburden benches of the working side of the mine, which showed constant differences in their structure and texture along the mining front. The expected differences and variability of the physical and mechanical properties of rocks were confirmed by the laboratory study of rock samples taken from the open-pit face. It is found that natural geological inhomogeneity of the overburden properties significantly affects the sequence and processes of drilling, blasting, excavation, transportation and dumping operations. Fracturing of the rock mass enhances the influence on these processes, general and local geomechanical stability of mine workings.

The trends of improving the technology of stope mining are determined, taking into account the design parameters of geotechnology and the figure of ore drawing. Efficient options of sublevel caving with rock preparation and rock pillar above the drill haulage horizon, as well as ore pretreatment are considered.

The use of the southern cage shaft of no. 11 mine within the structure of water-drainage system of M. Gorky Mine for water pumping using submersible pumps in order to ensure the safe operation of ground surface objects is substantiated.

The results of studying technogenic seismicity that arose in the area of open pit coal mining in the Novosibirsk region are presented. The mining intensity at the Gorlovskoye coal deposit increased significantly in the last decade and seismic activation of the subsoil of the Gorlovskaya depression is formed in response to the technogenic effect. Earthquakes with a magnitude of 4.5 experienced in Novosibirsk and its suburbs have been recorded in coal deposit area since 2019

A brief assessment of the mining, geological and geomechanical conditions for the development of production horizons of the Central Stocks section of the Kazskoye field is given. The analysis of rock pressure manifestation in a dynamic form is carried out. The stress-strain state of the rock mass has been diagnosed. The measurement results of strain increment level using depth and contour benchmarks are presented and the category of rockburst hazard is determined for different horizons. The stress-strain state of the rock mass was measured with the SB-32M device according to the parameters of acoustic emission. The time criteria for assessing the rockburst hazard were adjusted on the basis of comparing the results of recording the parameters of acoustic emission and the level of stresses obtained from the strain increment results at the stations of deep and contour benchmarks. A project has been developed for the installation of mobile seismic monitoring for recording events in stoping influence zone.

Tests and calculations were carried out, shear characteristics of the dump mass were estimated, taking into account several variants of landslide formation. The research results allowing to optimize the design parameters of external dump formation with a significant economic benefit are presented.

In this paper, the range of angles of the velocity vector of incoming air flow relative to the cross-sectional axis of ventilation connection between tunnels is determined by computational methods. Based on the data obtained, recommendations are given for the most rational dimensions, spatial location and installation angle of dust filter panels in the ventilation connection between tunnels.

In this paper, an approach to create reversible mine axial fan with inlet guide vanes is considered. In this approach, the guide vanes rotate and operate as an impeller in the reverse mode, while the impeller slows down and works as guide vanes. To increase the operating efficiency in the reverse mode, the blades of the impeller and inlet guide vanes are turned at certain angles not exceeding 65°. To determine the turning angles of blades in the reverse mode, theoretical dependences were used, according to which the angles of flow rotation in flat gratings composed of blade profiles were calculated at the middle radius. The range of turning angles of the blades for the reverse mode is determined for fan configurations with a hub tip ratio of 0.6 at different flow and theoretical pressure coefficients. The characteristic in the reverse mode is numerically determined by the example of one fan.

The relevance of studying short-period rock displacements and estimating the stress-strain state of the rock mass in rockburst-hazardous deposits is shown. The observation procedure using satellite geodesy methods is set forth. The results of continuous hours-long monitoring the shear of the Earth’s surface at the Tashtagol deposit for the period of 2006 - 2020 are presented. The features of the development of short-period displacements during seismic activity manifestation of the rock mass in the deposit area are revealed. The dependence of the energy of seismic events on the velocities of short-period displacements is determined. This observation method is prospective in geodynamic test sites to assess the seismic activity of deposits.

The paper presents the results of computational modeling of evaporative cooling of tunnel air during the phase transition of water from a liquid to a gaseous state in subway tunnel conditions at various parameters of spraying equipment. It is shown that this method significantly reduces the requirements for ventilation equipment in comparison with the method of removing heat excesses by ventilation alone. To remove heat excesses by ventilation alone, the capacity of one fan (with two fans running in parallel) is up to 269 m³/s, and the power is 727 kW. When using evaporative air cooling, the maximum capacity of one fan is 67.5 m³/s with a power of 104 kW, the pump power does not exceed 50 kW with a maximum water flow rate of 1.5 m³/h.

The idea of selecting and justifying the technology options based on a rating approach to the analysis of determining factors for the safety and efficiency of mining operations is considered with regard to the class of mining systems with caving of ore and enclosing rocks. A formalized method of the scoring system has been developed, which makes it possible to quickly make decisions regarding the use of geotechnologies based on the predicted stability of mine workings, the amount of losses and dilution of ore, taking into account the value of recovered minerals. The domain of rational influence of sublevel and block caving in different mining, geological and geomechanical conditions has been determined.

The results of studying aerodynamic processes taking place in extended blind drifts are presented. The change in local aerodynamic resistance of area under study is shown at the supply and suction modes of mine ventilation. Based on the results of computational modeling, it is shown that sepa-rately installed longitudinal partitions allow ventilating blind drifts (up to 100 m) without using lo-cal mechanical ventilation due to the resulting ejection effect.