Home – Home – Jornals – Journal of Mining Sciences 2022 number 6

The authors discuss applicability of phase characteristics of surface waves in monitoring of underground openings and tunnels. The mathematical model of surface wave propagation along extended cavities is presented. The properties of the numerical solutions obtained using the model are analyzed, including the amplitude and frequency characteristics, and the phase and group velocities of the waves. It is possible to recover elastic properties of a medium using the dispersion curves of the phase velocities. The data of numerical modeling of surface wave propagation along cavities of different geometry using the method of finite spectral elements are presented. The calculated results of the axisymmetrical and three-dimensional problems of surface wave propagation along cavities are studied.

Bischofite rock samples from a well at the Vologda underground gas storage are subjected to rheological tests. The time curves of deformation are plotted at different axial and lateral stresses. A viscoelastic phenomenological model is proposed, and the equation to describe these dependences is obtained. Being developed and algorithmically implemented, the experimental data interpretation procedure allows determining rheological characteristics of test rocks at different stress ratios. It is found that rheological properties of bischofite weakly depend on depth.

The implementation stages of ground laser scanning of an open pit field and the obtained data processing in Maptek I-Site Studio are discussed as a case-study of Kentobe open pit mine of iron ore. The procedure of a digital geological-geomechanical model is described; the framework is a set of spatial points obtained from the laser scanning. The model enables a detailed study of geological structure of the pitwall rock mass, with regard to the structure and tectonics, as well as the physical and mechanical properties of rocks. Using the developed model, the authors estimated the pitwall stability and substantiated safe slope parameters for deeper mining.

To predict uniaxial compressive strength using the indirect techniques of the Schmidt hammer rebound number (N) and Point Load Index (PLI), it is required to have valid empirical equations based on rock types. This study is an attempt to address this issue by developing a model that is valid for various rock types. Three models, i.e. linear, power and quadratic, were tested on each rock type (sedimentary, ingenious and metamorphic). The highest correlation was achieved by the quadratic model. The generalized model showed the lowest correlation as against the individual models.

The authors estimate stress state in the support system and in rocks nearby a roadway driven in unstable rock mass and when the voids and cavities in the roadway roof are filled with hardening foam. The calculation includes an assumption that the support system, rocks and the hardening foam deform elastically. The stress distribution in the support system is determined at different heights of the rock cavity in the roof rocks in the roadway and at different initial stress state of rocks. The zones of potentially hazardous stress concentration in the support system are identified.

The article describes the lab-scale testing data on acoustic and seismic emission generated in hydraulic fracturing of a cement block under volumetric loading by nonequal stresses. The connection of the acoustic and seismic emission with the rate of injection of power fluid and the change in the fluid pressure in the course of the fracture initiation, growth and arrest is demonstrated. The authors recommend on improvement of receiving equipment and on using the research findings in the hydraulic fracturing control.

This study focuses on an impact wave generated in a uniaxially compressed granite sample by a pendulum hammer in the direction transversal to compression. The pressure was varied from zero to a pre-destructive value. Microcracking during impacts was recorded using the method of acoustic emission (AE). The energy distribution in the time series of AE pulses followed an exponential law both in the unloaded and in the statically loaded samples. The first impacts induced local damage with a splash in AE from small cracks which, under subsequent impacts, coalesced and initiated redistribution of larger microdamages. In generation of an impact wave in a sample under pre-limiting compression, the surface of the induced main crack exceeds the area of the local damages by a few orders of magnitude, which is typical of the trigger effects which lead to large-scale fractures under external impacts at a safe-density energy.

The scope of the experimental research embraces velocities of elastic waves in rock samples before and after formation of a horizontal main crack. In undamaged samples, there is no essential change in the elastic wave velocity as the axial pressure increases from 0 to 20 MPa. The main crack having its surfaces approaching gradually leads to the increase in the elastic wave velocity. Aimed to improve sensibility of kinematic ultrasonic parameters relative to mechanical stresses, the coda wave interferometry algorithm is implemented as an analysis of times of the first arrivals of multiply scattered waves. With the mentioned algorithm, sensibility of the ultrasonic control grows considerably even in uniform samples.

The article describes the decision-making concept for the systemic blasting in open pit mining at structurally complex mineral deposits. The authors discuss approaches to determining allowable seismic impact in rocks having different strength characteristics.

The article describes semi-commercial testing of different technologies and facilities which ensure the required level of mining efficiency and quality of diamond-bearing ore. The use of the column charge explosives with radial clearance and air-split emulsion explosives allows stress state control in rock mass and reduces zones of high risk of crystal damage. The chain charge explosives appear to be a clever engineering idea for difficult mining conditions. The authors review the modern methods of drilling-and-blasting at mining sites of ALROSA.

The seismic activity in undermined rock mass in a mine at the Khibiny Massif is analyzed over the period from 2008 to 2020. The influences on deformation, tensile fracturing and caving in undermined rock mass are revealed. Three zones of deformation of different nature and velocity are identified in undermined rock mass in Kirov Mine: the zone at the juncture of underground and opencast mining; the zone of overhanging rocks; the zone of two- and three-side buttress at the edges of operating deposits. It is found that mining with head-on fronts, with formation of a support pillar and with overhanging of an uncaved rock mass beam is adverse. The pillar collapses later on and deformation of the pillar-supported rock mass during breaking of the butt section on sublevels occurs in the dynamic mode with high seismic activity both in terms of the number of seismic events and their energy emission. It is found that the width of the seismic activity band and the caving pitch of the overhang depend on the height of undermined rock mass.

The authors review the application range and parameters of internal dumping in open pit mining of brachysyncline-type coalfields. Specifics of the technology is described. The factors that govern the volume of internal dumping are identified. The possible ways of increasing the volume of internal dumping are shown. The methods and means for increasing the intake capacity of internal dumps are revealed. The ecological and economic advantages of internal dumping are discussed.

For structurally complex orebodies in weak zones of enclosing rock mass, a variant of the sublevel stoping technology with cemented paste backfill is proposed. On the ground of the in-situ data, the analytical relations are constructed to determine stability of artificial roof and sidewalls in stopes. It is found that backfill possessing the uniaxial compressive strength of 3 MPa preserves stability in the course of extraction of ore from adjacent stopes and in mining on the lower lying level. The recommendations on backfilling are given.

The article highlights the urgency of studying processes of deformation, displacement and collapse of undermined strata at rockburst-hazardous deposits of the Khibiny Massif with regard to geomechanical and geodynamic risks. The authors analyze failure specifics in undermined strata under the action of tectonic stresses, which consists in impeding of fracturing due to subhorizontal compression. It is found that as the thickness of ore bodies decreases and their dip angle grows at great depths, the pitch of failure increases. The problems to be solved to continue extraction of apatite-nepheline ore at minimized induced risks and at the preserved economic efficiency are listed.

The authors investigate thermal processes in an electromagnetic percussion assembly of a downhole pulse vibration exciter at the rated energy mode in the naturally cooled air environment and at different methods of heat energy transmission from the coil to the body. The interrelation is found between the coil and body temperature, external cooling, duty cycle and the coil-body expansion gap when it is filled with air or oil. Based on the obtained results, the duty cycle of the vibration exciter in a well is calculated when the body of the electromagnetic percussion assembly is cooled with flow water.

The authors discuss concentration of fluorite from waste at Yaroslavskaya Mining Company. The waste accumulated in the tailings storage for the long operating period contain 11.6-20.7% of fluorite. Old tailings have specific process properties because the initial ore has experienced certain physicochemical treatment during primary processing, and owing to long storage. The package of balanced effects which ensure selective recovery of fluorite is substantiated. The obtained concentrates contain up to 95% CaF₂. Production of fluorite concentrates at maximal removal of silicon dioxide, which is a strictly restricted impurity, is discussed. The ways of improving the processing circuit are proposed, and the efficiency of electrochemical treatment of the pulp fluid phase at the final stages of recleaning is proved. It is found to be possible to reduce the silicon dioxide content of the concentrates to 1.25-0.99%.

The article describes the studies into the process of upward mass transfer in flotation tailings with water solutions. The swift-flowing geological process is investigated using the magnetic resonance imaging. The kinetics of water-soluble minerals as well as the structure and substance transformations in the body of tailings are studied for substantiating in-situ formation of the target concentration zones at the tailings surface.

The article gives a review of scientific publications and regulatory documents connected with reclamation activities at the sites of waste storage in the mining industry in the Russian Federation. The environmental, economic and social impacts of mining are discussed. The role of reclamation in the recovery of the disturbed lands and ecosystems is illustrated, and the methods and stages of reclamation are described. The main obstacles of reclamation to be successive are revealed. It is highlighted that the spotlight should be on improvement of reclamation legislation to enhance efficiency of rehabilitation measures.

The author focuses on the measurement and recording equipment for the laboratory research of hydraulic fracturing in the conditions of rock pressure simulation. The choice of the test values, discretization intervals and observation periodicity is substantiated. The functional flows of the program code in LabView are presented. The program code ensures synchronous multi-point measurements of deformation, breakdown pressure, acoustic and seismic emission, power fluid flow rate, etc. The recommendations on selecting equipment, sensors and research findings for designing measurement and monitoring systems for geodynamic processes are given.