Home – Home – Jornals – Fundamental and applied issues of mining 2019 number 1

Numerical modeling was performed for stress-strain state of the rock mass and lining of underground turbine hall of Rogun hydropower plant. The hall is located in a rock mass at great depths. Numerical modeling was conducted using the method of boundary integral equations based on the model of linearly elastic quasi-isotropic medium. The character and features of forming inelastic deformation zones near the contour of turbine hall cross-section are found. The regularities of distribution of rock mass and lining stress-strain state are determined as well.

The paper discusses the stress distribution in the vicinity of an uncased borehole during hydraulic fracturing. Fixed bridges made of polymeric material are used as sealing elements. The applied mathematical model takes into account piston displacement of bridges when pressure is applied to an isolated interval. The results obtained allow optimization of engineering solutions of in-mine hydraulic fracturing to intensify the degassing of coal seams.

Seismic data filtering algorithm has been developed. The proposed algorithm allows amplifying signals from the sources located inside a selected area of space. The paper presents a theory describing the principle of this algorithm. Testing on synthetic data showed that the proposed filtering method is capable to suppress signals from the sources located outside the selected area of space. On semi-synthetic data it was shown that the proposed filtering method allowed to suppress real noise and significantly increases the signal-to-noise ratio for the events located inside a selected area of space.

The behavior of a hydraulic fracture near the mine opening in a plane-parallel formulation has been investigated. The case was considered, when the rock was under hydrostatic pressure, and the initiating crack was oriented in the direction of mine opening. It is found that the fracture path is greatly influenced by the ratio of hydrostatic pressure and critical tensile stress of rock. It is shown that when the hydrostatic pressure increases with respect to critical tensile stress, the fracture begins to deviate from the mine opening earlier and does not reach its surface. It is also shown that under various conditions, fractures cannot bypass the mine opening completely due to the occurrence of severe strains in the area between the opening and fracture

The propagation of surface pendulum waves under nonstationary loading on the free surface of a cavity located in a block half-space is studied numerically. A mathematical model of transient viscoelastic deformation of the block medium is proposed. This model is based on the idea that dynamic behavior of the block medium can be approximately described as the movement of rigid blocks due to the compliance of interlayers between them. To describe the viscoelastic behavior of the interlayers, an internal friction model is used with the merit factor of the material as the determining parameter. The medium is modeled by a three-dimensional lattice of masses connected by elastic springs and viscous dampers in axial and diagonal directions. The influence of the merit factor and the cavity depth on the amplitudes of block velocities on the surface of the half-space is investigated for the longitudinal and Rayleigh waves.

The model of linear elastic theory with structural parameter has been used in present paper. In plane formulation, the constitutive relationship system consists of five independent equations, whereas there are only three equations in classical elasticity theory. Two remaining equations are implicitly contained in the postulate of diffeomorphism-an assumption about smoothness of displacement field. Refusing the postulate of diffeomorphism introduces a structural parameter in the model-macrodeformations which depend on stresses and second derivatives of stresses with respect to coordinates. The boundary value problem of pillar deformation taking into account the influence of surrounding rock mass has been formulated and numerically solved.

An analytical method has been developed for determining the stress state of monolithic support of parallel mine workings constructed by a closed method near an inclined Earth's surface. The influence of the Earth's surface inclination angle and mutual location of mine openings on the formation of stresses in the support of openings has been considered.

The model of lithospheric geodynamics is considered within a problem on viscoelastic litosphere deformation under the influence of inertial rotation forces and viscous forces of spherical Couette flow in an astenosphere. This flow determines the nature of internal geodynamic pressure and tangential stresses. Depending on the difference of angular velocities of lithosphere and mantle rotation, the lithospheric shell can be in comprehensive expansion or compression conditions. The mechanism of local changes in the litosphere thickness as a result of instability of deformation of the Earth’s lithospheric shell under the influence of internal pressure and volume inertial forces of rotation is found. Loss of deformation stability is investigated by the Leibenzon-Ishlinskiy’s method. Within a viscoelastic rheology of litosphere, the stress-strain state of a litospheric plate under bilateral compression is analyzed.

The paper considers a promising method for determining stresses in rocks based on the Kaiser effect. The analysis of various models of crack formation causing the manifestation of this effect was made. It is shown that one of the reasons for the occurrence of this phenomenon in the case of initial core loading can be the activation of cracks, which formed during unloading of the rock from effective stresses in the rock mass.

This paper discusses the possibilities of structural interpretation of space images and morphometric analysis of the latest tectonic movements, which are still poorly studied in the oil-and-gas bearing area of the junction of the Ustyurt (Takhtakairsky ridge) and the north-western part of the Bukhara-Khiva region (Khorezm monocline and Mishklinsk uplifting, Dashkalinsk and Birgutli-Shortaklinsk troughs). As a result, lineament and “strip” geodynamic zones of abnormal fracturing were identified. Their formation is probably associated with the accumulation of diagonal stresses of the gradient zones of structural-tectonic framework, within which fault-block structures are distinguished. Morphometric analysis showed that under the influence of modern tectonics, local positive structures with predominantly gas-filled traps correspond to areas of maximum activation.

The possibility to obtain the information on the flow of mechanical processes in geomaterials beyond the limits of elastic deformation using the variations in the IR radiation intensity was studied. The results of experiments on recording the parameters of thermal radiation from the surface of rock salt and concrete samples at close to limiting periodic loading conditions under uniaxial compression are presented. The qualitative identity of the records of mechanical parameters and thermal radiation variations characterizing changes in the stress-strain state of the tested geomaterial samples is shown. The differences in the recorded manifestations of thermomechanical effects in concrete and rock salt under the specified deformation mode are established.

Algorithm has been developed for configuring the observational network of geomechanical monitoring system of rock pressure. A software module has been developed based on the algorithm, which allows to draw sensitivity maps of the spatial zone and adjust parameters of the geophone network. Possibility of drawing maps using control levels of the uncontrolled zone, non-guaranteed and guaranteed control zones has been implemented. These zones show confidence of seismic acoustic signals location by geomechanical system. Procedure has been developed to select number and location of geophones. Main directions are formulated for further improvement of the algorithm for observation network configuring.

Based on experimental studies, it was found that taking into account the influence of rock anisotropy allows to improve the location quality by 10 - 20%. It is shown that for processing the results of seismoacoustic monitoring with regard to anisotropy in the controlled area, it is necessary to develop specialized software that implements a velocity model of the wave propagation medium. Approaches to its development and implementation have been formulated. This will improve the location accuracy and, as a result, the quality and reliability of forecast estimates when conducting geomechanical monitoring of a shock hazardous rock mass due to more accurate identification of potentially dangerous seismoacoustic active zones.

A new analytical method is proposed for seismic analysis of multilayer linings in shallow tunnels. The method allows taking into account the influence of seismic waves reflected from the Earth's surface and Rayleigh waves. The most hazardous stress state that may take place in radial sections of the lining during the earthquake of given intensity is determined. As an example, the seismic analysis is performed for the lining of a tunnel located in a seismically active area. The envelope diagrams of maximal values of tensile and compressive stresses along internal outline of the lining cross section and corresponding diagrams of longitudinal forces and bending moments in the lining are constructed. The dependences of the maximum stresses arising in the lining during the earthquake on the tunnel depth are obtained and analyzed.

The diagrams for supporting workings by floor and roof bolts are considered, which allow to reduce the swelling of floor rocks and manifestations of rock pressure. The degree of influence of mining and engineering factors on the bolting effectiveness of workings is established.

The regularities of changes in the stress-strain state of coal in rock mass depending on the main mining geological and engineering factors are identified. Using these factors, it is possible to find the optimal support parameters in specific conditions to increase the stability of preparatory mine workings. The degree of influence of mining and engineering conditions of exploitation on displacements in marginal rocks with various types of support in excavation workings is investigated.

A measuring system has been developed for a test bench allowing the study of gas-dynamic processes in large-sized rock samples when performing hydraulic fracturing of a coal seam in a borehole model. This system provides collection of the data on pressure in a hydraulic fracturing device and loading of pneumatic jacks which create compressive stresses in the borehole zone, it also records acoustic emission during crack formation. An additional capability is implemented to measure the flow rate of gas suppled to sample through the holes on its side wall and pumped from the borehole.

The development of limiting states near a mine in a transversally isotropic (layered) massif of complex structure is considered. In the elastic zone, the massif has an anisotropic structure and obeys the generalized Hooke’s law, and in the plastic zone it is assumed isotropic. When determining the plastic zones, the Hoek-Brown failure criterion was used for the first time. The problem is solved approximately by the P.I. Perlin’s semi-inverse method using an iterative scheme. A system of algebraic equations is constructed to find the unknown coefficients of the complex potential. The values of displacements in a plastic zone are found using the characteristics method.

The impact of seismic vibrations from blasting in the Biyankovsky gravel pit and from passing trains on the rock mass has been estimated. The beginning of work is associated with an accident that occurred in summer of 2017, as a result of which two carriages derailed. The fractured structure of the rock mass was studied, and sustainability of hard rock mass jointings within the Ashinsk track maintenance section was estimated. It was established that recorded seismic vibrations in rockfall areas were less dangerous for disturbing the rock stability than the geological features of hard rock mass, which caused inrush. Recommendations are given to prevent rock debris from rolling out onto railroad tracks.

The study results of rock properties of Zhdanovsky copper-nickel deposit are presented in the article. The deposit is located in Pechenga district of the Murmansk region. The main purpose of the work was to determine the nature of the elastic energy accumulation in the rock samples studied and to assess their proneness to dynamic uncontrolled failure. Based on the performed experimental studies, the mechanical properties and energy parameters of the samples under uniaxial and triaxial compression conditions were determined. The analysis of the results has shown that the studied rocks belong to the hard rocks which are prone to dynamic failure. It is one of the conditions for classifying the deposits as rockburst hazardous.

A three-dimensional model of a probabilistic cellular automaton, which was previously constructed on the basis of the kinetic theory of strength, is studied in this paper. It describes the process of rock damage accumulation and formation of a damage cluster structure. Comparing the kinetic curves of damage accumulation and correlation functions by means of model experiments, it was found that, depending on the probability of germination of the damage cluster perimeter, which simulates the intensity of material failure under the action of local overstresses near the existing damage clusters, two qualitatively different modes of damage accumulation are observed for a three-dimensional model. For the probabilities of germination of the cluster perimeter exceeding the value of 0.2, the process of transition to irreversible failure is significantly accelerated and becomes strongly correlated. Along with this, the best correspondence of correlation functions in model and physical experiments is observed for perimeter germination probability values smaller than 0.2.

The problem on elastoplastic deformation and rock failure around boreholes under the action of internal pressure is considered. The stress state in the intact rock mass is assumed to be hydrostatic. The hydraulic fracturing pressure is conventionally determined by the maximum normal stress criterion. However, the experimental studies described in scientific articles show that this criterion is not consistent with the results obtained in the course of laboratory tests on failure of cylindrical and spherical cavities made in rock samples. It has been known that test results on complex loading for solid samples of various materials are not confirmed by the theory of maximum normal stress both in terms of ultimate load value and direction of failure surface propagation. In this case, for the complex stress state of rocks, it is proposed to determine the ultimate pressure by the experimentally substantiated fracture criteria which are in good agreement with the results of laboratory tests on hydraulic fracturing of boreholes.

The identified features of the development of geomechanical processes in the massifs with block structure in open-pit mining of gold deposits in Kyrgyzstan are analyzed and their influence on the stability of open pit walls is determined.

The possibilities and results of using the methods of X-ray computer microtomography, ultrasonic measurements, nano-and microindentation, control of submicronic particles formation applicably to studying dynamic rock failure are discussed. The X-ray computer microtomography was used for studying pore and microcrack distribution in the sample volume. The ultrasonic method was applied to control the condition of samples before and after dynamic effect. The method of micro-and nanoindentation helped to determine hardness, Young’s modulus at various scale levels, and failure viscosity. The patterns of submicronic particle formation during the coal samples failure under dynamic effect are investigated. It is shown that investigation results are important for geomechanical support of mining operations, including studying such phenomena as rock bursts, sudden coal and gas outbursts.

The influence of a crack formed in the opening roof on stress-strain state of the rock mass is considered. The relationships determining displacement and stress components at the boundary of an opening with rectangular shape, on contact lines of the layers and on the line containing crack are written. The examples of numerical implementation are given. The analysis of the obtained results is carried out.

The issues of obtaining and investigating composites consisting of coal and rock solid particles, gases (methane, hydrogen) and moisture, as well as approaches to mechanisms initiating catastrophic dynamic phenomena in mining are discussed. On the samples of different materials (coal, limestone, graphite, etc.) using the developed test bench, the dependences of physico-mechanical properties of cores on pressure are established. For longflame coal of various size, the features are shown for changing the temperature of briquette mass in increasing pressure up to 200 MPa. The composites imitating natural coal and other rocks are created.

The paper reviews a new approach to quantitative geotechnical risk assessment. This approach is applicable to a preliminary rough risk assessment based on a simplified quantitative classification of hazards for tunnel projects. We consider its applicability on the example of the railway tunnels on the Baikal-Amur Mainline. Quantitative risk assessment for the BAM tunnels is performed retrospectively - mainly the design and construction stages are taken into account. The expediency of developing similar algorithms for a more detailed assessment and forecasting of current geotechnical risks, as well as for the dynamic control of risk level changes during construction and operation using the integrated geotechnical monitoring system for both transport tunnels and other underground structures has been proved.

Actual issues of improving the design of the downhole probe as part of equipment for the practical implementation of the method of measuring hydraulic fracturing in mine conditions were discussed. The variants of the probe operation control schemes are presented using a single press pipeline, designed to simplify the installation of the equipment in the borehole, especially at considerable distances from the working contour. The new design map for controlling the process of probe packing is considered. Its application eliminates unstable deformation of sealing elements, in case of the well diameter increase above the nominal value, ensuring reliable sealing of the test area.

The problem of exposure stability of blind ore bodies which are mined by the systems with a collapse of ores and enclosing rocks in difficult mining and geological conditions is considered. The results of monitoring the processes of displacement and deformation of the Earth’s surface over the mined-out space of blind ore bodies, where the protected objects are located, are presented. Anomalous parameters of vertical and horizontal displacements, high short-period movements during large-scale blasting were established. Particular attention is paid to the parameters of displacement of the Earth’s surface above the future pit before its formation, which were significantly lower than the criteria values. The factors which influenced the pit formation are analyzed.

This paper discusses using high-precision GPS observations to compute the velocities of points on the surface of mountain massif of any scale and surrounding territories. It describes the existing technology and method for computing velocities and coordinate time series of geodetic benchmarks using GPS observation data. Then, the problems that hinder to obtain most possible precise results of this computation are reviewed in this paper. Finally, it suggests the tools to automate stages of this method that haven’t been previously automated, these tools multiply decrease labor intensity in solving these problems and applying this method in general.

This paper is devoted to the study of wave propagation in elastic viscoplastic layer with a cavity, located on an elastic base under the dynamic pressure of day surface. This problem is solved by “discontinuity disintegration” method of S. K. Godunov. Using the S. K. Godunov’s method for research and solution of wave propagation in a layered semi-sphere with cavities located on an elastic base under the dynamic pressure will further develop the solution to the same types of problems in other mechanics subdisciplines.

An approach has been applied, according to which the electromagnetic field of endogenous origin is included in the impedance relations in an additive way, which allows to separate the electromagnetic field recorded on the day surface in compliance with the position of sources. Practical examples of distinguishing an electromagnetic field of endogenous origin in field recordings of magnetotelluric soundings performed in the Tien Shan region are presented. The characteristics of the distinguished electromagnetic field of endogenous origin are compared with the parameters of lunar-solar tides and anisotropic properties of electrical resistance The detected relationships of these parameters indicate new possibilities for studying permanent deformations in the Tien Shan lithosphere using magnetotelluric data.

The hypothesis of a linear stress field of a rock mass undisturbed by driving workings underlies the solution to many problems of rock mechanics. The problem of rock pressure control requires knowledge of the stress-strain state of the rock mass in the vicinity of workings, which causes the development of analytical and numerical methods for calculating the deformation. When the methods of numerical calculation were not sufficiently developed, the analytical capabilities of the selection of stress functions were used, which satisfied the conditions of small strain elasticity theory. The greatest success in this direction was achieved for the areas with angular points. The development of numerical methods shifted the point of influence of investigations to calculating the deformation of specific cases arising in a rock mass with workings. It is established in the work that analytical solutions for the areas with angular points are incorrect, and numerical solutions of Cauchy problems are also incorrect if an additional problem is not considered.

Solution of elastic problem for half-plane is of the highest concern in almost every field of engineering. However, there are no relations binding the values of all components of the stress-strain state at the half-plane boundary This paper shows that arbitrary formulation of the boundary conditions considerably simplifies integral equations and transfers them to the class of Fredholm’s first kind equations. Considering symmetry, the problem for half-plane with mathematical cut is reduced to the problem on half-plane boundary. Regardless of the method, any solution is reduced to ill-posed problem.

Experimental results of seismoacoustic monitoring of the rock mass in a longwall are analysed for different cases of rock bumps. Characteristic values and parameters of acoustic emission and convergence of the face are accepted as predictive parameters of the rock mass state.

Hydraulic fracturing is a promising method used for increasing the permeability of a coal seam. Formation of an extensive network of drainage cracks contributes to increased gas recovery of coal. In this case, a negative factor is the breakthrough of cracks formed in the mine workings. In order to challenge this problem, it is proposed to screen mine workings with an additional crack filled with acrylate polymer containing solid inclusions, which prevents the closure of crack edges under the impact of rock pressure. The paper presents the results of experimental studies of acrylate screen gas permeability dependence on rock pressure.

A thermostatic plant for studying the adsorptive capacity and permeability of coal core was developed. The plant design allows to saturate coal with methane and to filter gas at various values of axial and lateral compression of the sample. The use of an automated system for recording differential pressure and gas volumes in the inlet and outlet tanks eliminates the need for manual control, which is especially important during long-term testing of low-permeable coals.

A new analytical method for estimating the stress state of a rock mass composed of two types of rocks with a straight-line boundary near a supported circular opening is proposed. The method is based on a strict solution of the plane problem of elasticity theory for an infinite weighty medium composed of two different materials and weakened near the rock interface by supported circular opening. The obtained solution is based on the theory of analytical functions of complex variables, properties of Cauchy-type integrals and complex series. An example of stress distribution in the rock mass near the opening is considered. A comparative analysis of the calculation results obtained in accordance with the proposed method and the data of FEM computer simulation are discussed.

The effect produced by hydraulic fracturing on the filtration resistance of coal seam zone subject to drainage by parallel boreholes is considered. The resistances to the gas inflow depending on the orientation of fractures, thickness of seam, and distance between the boreholes are analyzed. The efficiency of single and multistage hydraulic fracturing in forming multiple transverse and main longitudinal cracks is compared.

The methods based on the use of time-frequency representations are proposed. The usefull signal is reconstructed from the amplitude peaks of time-frequency spectrograms obtained by S-transform. As a result of numerical experiments, it is shown that using narrow time-frequency intervals (about 10 - 20 time reports), it is possible to determine the parameters of a pulsed-type signal with substantially longer duration