Home – Home – Jornals – Journal of Mining Sciences 2020 number 5

Shock wave travel in a roadway with impermeable safety barriers is modeled numerically in the equilibrium and non-viscous formulation. Inclined and arched barriers are studied at the varied porosity in a range from 0 to 0.8. The inclined and arched barriers decrease the load exerted on the barrier structure by the shock wave owing to formation of a reflected wave which is oblique, or radial in case of the arched barrier. An increase in porosity of the barrier can additionally weaken the shock wave effect but barriers with high penetrability make the defensive screen inefficient, which is confirmed by the higher differential pressure at the shock wave front after passing the barrier.

The article describes the experimental studies into hydraulic fracturing of thick-walled cylinders with a circular hole and made of cement-based GF-177 mixture. Limiting stresses are determined in four types of stress state of the bodies: uniaxial compression and tension, Brazilian Test and hydraulic fracturing. The data of the Brazilian Test and compression of rectangular parallelepipeds and circular cylinders were used to determine limiting pressure in hydraulic fracturing. The critical stress intensity factor is found. The calculated limiting pressures are compared with the values found analytically from the Lamé solution and with the test data. The influence of the storage interval on the strength is described.

The thermal and mechanical tests of different porosity limestone show that an increase in the axial load results in the higher velocities of elastic waves while elevation of temperature decreases them. Higher temperatures act to raise velocities of P- and S-waves with increasing mechanical load, which enhances acoustic strain-sensitivity of rock. The spectral analysis of the recorded signals shows that higher temperature shifts spectrum maxima to lower frequency region. It is found that size of pores has influence on attenuation frequency of ultrasonic signals. The authors describe new approaches to acoustic strain-sensitivity control in rocks and to stress measurement reliability enhancement toward stability of underground structures.

The research methodology for anisotropic permeability of geomaterials due to nonuniform stress state is theoretically justified and tested on a laboratory scale. The poroperm properties of fine grain sand and cryogel are investigated in diametral compression tests of cylindrical specimens with a center hole. The time-independent flow rate is measured in various areas of side surfaces of the specimens. The inverse coefficient problem on empirical permeability-effective stress relationship is formulated, and its solvability is demonstrated.

The author solves the problem connected with determination of shape of pillars which remain stable under any compression due to barrel distortion. The analysis of cylindrical structures uses the known Leibenson-Ishlinsky stability criterion. The boundary conditions of the problem and its solution are obtained: elasticity in the form of the critical load dependence on the height/radius ratio of pillars. The found asymptote to the curves is associated with the optimized shape of pillars.

In hydraulic fracturing of producing formations in oil and gas reservoir engineering, as well as in coal gas drainage, hydraulic fractures are propped by solid particles-proppant that prevents closure of fractures under the action of compressive stresses in rocks. It is shown that alongside with lateral earth pressure, the compressive stresses in fractures are governed by additional compression generated by fracturing and by compression of rock in depression zone formed in the reservoir fluid inflow to the fracture. The compressive effect in the depression zone can be adjusted by reducing the rate of depression growth in time. This method of compression decrease in fractures is the most efficient in reservoir engineering and in shallow coal seam gas drainage. The compressive stresses in the depression zone are comparable with the lateral earth pressure, thus, the differential pressure step-up can make it possible to keep the stress-strain behavior of rock in the neighborhood of a hydraulic fracture within the limits of elastic deformation and to prevent the fracture closure with irreversible pressing-in of proppant in rock.

The article describes the long-term in-situ observations and inspection of concrete lining in air inlet shaft No. 3 in Uralkali’s mine, which reveal the main causes of the lining failure at intersections with horizontal tunnels and in the areas of instable rocks. Numerical modeling of rock creeping and damage areas in lining at intersections with tunnels is performed in the axially symmetric and three-dimensional formulations. The calculations agree with the observation data, which proves efficiency of mathematical modeling in estimation of deformation and failure of concrete lining during shaft design and operation. Prediction of damage evolution in concrete lining in shaft No. 3 is carried out for the next 10 years.

The slope stability evaluation using the generalized Hoek-Brown criterion and with regard to the scale effect has been implemented in terms of the Chaarat gold project. Furthermore, the probabilistic assessment and sensitivity analysis are performed. Landslide probabilities are determined, and the slope stability factors are obtained as functions of the slope height and angle. The slope stability estimation procedure synthesizing classical approaches with regard to the scale effect, including GSI and probabilistic analysis is tested in rock ground. Slope stability is mainly governed by variability of the Geological Strength Index related with the scale effect.

The authors discuss the mechanism of breaking coal by blasting with a view to optimizing this method of dynamic treatment of coal and improving drilling-and-basting performance. A combination model of high gassy coal is used to describe the connection between coal breaking by blasting and subsequent gas liberation. This model and the smoothed-particle hydrodynamics method are used to study evolution of damage zones and stress-strain behavior of coal in the neighborhood of a blasthole after explosion. The research findings help predict coal response to the dynamic impact.

The authors present a new rock fracability evaluation procedure using the cluster analysis of log data on petrophysical properties of facies. The effect of the physical and mechanical properties of rocks on the fracability evaluation results is analyzed in combination with the geophysical log data. The triaxial compression tests of cores are carried out to determine their brittleness indices. An entry-level classification of petrophysical properties of rock facies is implemented by the cluster analysis of the geophysical log curves. A new classification procedure is proposed for the petro facies analysis using the permeability index and brittleness index of rocks, and the profile of rock fracablity index is obtained. Application of the procedure is illustrated using core data from a reservoir in China. The fracability index of cores sampled in a horizontal well correlates well with the calculated profile of fracability index.

In this study, Time Domain Reflectometry (TDR) is engaged to observe coaxial cable deformity caused by slope movements. Laboratory shear tests were executed to measure the deformity magnitude caused by shear failure using two coaxial cables-RG-6 and RG-213. Two assessments are performed in laboratory testing, to determine the deformity magnitude-shear test and Open-Cast (OC) model. For shear test, two regression methods are computed-linear and quadratic regression. The quadratic regression results show more effective positive correlation with shear deformity as compared to linear regression results. For RG-6 and RG-213 cables, the average highest magnitude of coaxial cable deformity by shear failure is 11 mm and 14 mm, respectively, which are equivalent to Reflection Coefficient (RC) of 0.49 and 0.050 for RG-6 and RG-213, respectively, beyond which the cable breached. Field tests are also performed which concluded that TDR is the most preferable technique to monitor slopes of OC mines.

This paper describes the development of statistical models for assessing the boulder count resulting from the limestone quarry blasting. A database of three hundred blasts was created for the development of the model. The database consists of number of holes per row, number of rows, average spacing, average burden, average depth, average stemming, explosive type, total charge fired in one round and the boulder count. All the variables in the database are ratio type except the type of the explosive which is a nominal variable. Hence two distinct statistical models have been developed for the ANFO and the SME blasts. The models have been developed in SPSS 20.0. The Student’s T-Tests and Fisher’s Exact Tests have been carried out on the models to identify the significant variables. It is further found that the prediction capability of the statistical models is strong and it provides an easy option to the field engineers to assess the blast design for the boulder-count. The developed statistical models are suitable for practical use at the limestone quarries having similar geotechnical set up.

The author addresses a method of creating directional conjugated fractures in a solid medium, integrating features of interaction of fractures and holes, specifics of fracturing by plastic materials and the use of holes as the front guides and limiters of created fractures. This method can be used to enhance efficiency of open pit and underground mining, as well as for creation of closed impermeable envelopes for advancement of slot mining technologies without construction of underground mines.

The authors analyze gas control readings obtained in Butovskaya Mine, Kemerovo Region, in step-down phase of seismicity and after blasting operations. It is estimated how seismic waves induced by blasting influences methane drainage in coal seams. It is found that methane release from coal seam to roadways increases after seismic impact.

It is technologically and economically advisable to optimize grading of low-quality fine and very fine sand with increased content of clay and dust particles used in preparation of cemented backfill mixtures by adding blast-furnace granular slag screenings 0-5 mm in size without preliminary treatment. The relationships of the size modulus, specific grain area and clay/dust particle content of sand and the percentage of slag in the composite aggregate are obtained. It is found that with increasing percentage of slag in the composite aggregate, water demand lowers owing to the higher size modulus of the aggregate and due to the decreased content of clay particles in it. This allows production of cemented backfill mixtures at the decreased consumption of cement while the strength and flowability of the mixtures are preserved.

Modern heavy-duty shearers cut coal with high production of dust particles. The screen tests of coal from Zarechnaya Mine are reported. Methane flow rate is theoretically calculated as function of dispersion phase in coal from Zarechnaya Mine at different particle size distribution of coal. It is found that methane flow rate reaches its maximum in fine coal 0-25 mm in size.

Advancement of wave action stimulation and cross-well seismic imaging in mineral mining governs the need for downhole sources of elastic vibrations. The presented periodic electromagnetic seismic source is equipped with a mechanical-hydraulic drive for fixturing in a hole and for impulse transition to rock, and an electromagnetic impactor for pressure pulse generation. This article presents the experimental studies into the operation of the seismic source of three structural layouts. The features of the operation are discussed. The supply voltage dependences of the main parameters of the seismic source are obtained, and the practical application recommendations are formulated.

The experimental studies into stimulation of chemical and electrochemical leaching of gold from rebellious concentrates by ultrasound are presented. From the assessed efficiency of saturation of chloride solutions with electrochemically activated chlorine and the analysis of change in the surface morphology and in the composition of elements, phases and particle sizes in concentrates, the leaching stimulation mechanism is determined and the efficient ultrasonic treatment parameters are found for a mineral suspension to ensure higher gold recovery by 39% in 5 h.

It is suggested to improve selective milling and disintegration of mineral associations of mining waste by means of stage-wise increase in destructive energy. It is found that relative frequency of opposite rotation of rotors and the number of pass cycles of waste through disintegrator can be of use in optimization of separation of preset size fraction at minimized loss of spodumene owing to the reduction in slurrying. The flow chart is developed for the stage-wise disintegration of spodumene-bearing mining waste with obtaining of product of flotation size - 0.16 + 0.02 mm at minimal yield (6.0%) of slime fraction - 0.02 mm. The proposed flow chart efficiency is proved by the flotation concentration results.

Dispersiveness of emulsion composed of oily reagents is estimated using the method of laser diffraction in experimental and in-process tests of flotation of slurry coal. Effect of agitation level in emulsification on emulsion dispersiveness and on flotation of different size coal of two grades is described. It is found that emulsification of oily reagents has influence on flotation efficiency. Increased dispersiveness of thermal gasoil and waste motor oil emulsion exerts a beneficial influence on flotation of coarse and fine coal of the both grades while flotation quality with waste motor oil emulsion worsens. It is possible that selectivity of separation of coarse and less hydrophobic coal also decreases.

In this study, the changes in the specific rate of breakage and breakage distribution function of the nepheline syenite sample were investigated by using alloy steel ball in five different sizes. Specific rate of breakage and breakage distribution function values were obtained from the particle size distributions acquired after the grinding periods. As a result of grinding tests, an increase in rate of breakage is observed due to the increase in ball diameter.

The authors discuss artificial freezing of water-saturated rock mass during construction of mine shafts in terms of a simplified case of a single freezing pipe. The ice growing and holding stages are examined. Maintenance of a constant thickness frozen wall is simulated using the coolant temperature sensor model. The multi-criterion numerical modeling of freezing is implemented, and the time dependences are obtained for the coolant temperature at the ice holding stage. It is found that maintenance of the constant thickness of frozen wall requires that the coolant temperature in ice holding is exponentially grown at the power around - 0.2. The ice growing stage temperature has no influence on the total energy efficiency of the freezing system.

The authors describe the structure, features and application of a software using the extended finite element method in ABAQUS. The software is meant for modeling hydraulic fracturing of permeable rock mass with fracture path tracing in nonuniform stress field.