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The spotlight of the analysis is on the elastic properties of dolomite and limestone host rocks of diamonds at the Botuoba Pipe in the conditions of partial saturation. Pre-saturated rock samples were subjected to three testing cycles during natural drying in room conditions. The change patterns in the elastic modulus of the test rock materials are determined subject to their water contents in different regimes of water saturation. The authors arrive to the conclusion that the prevailing concept of water effects on the mechanical properties of rocks is only valid in the steady-state conditions and is invalid in the unsteady-state conditions when moisture is nonuniformly distributed in the pore space of rocks.

The article describes the laboratory testing of permeability and structure of loose rock hardened with two-component highly elastic polyurethane resin at different methods of impregnation and at different consumptions of the polymer. Two methods of impregnation are tested: with a single solution as a mixture of two resin components and with a double solution of separate components mixed inside the test rock. It is shown that the decrease in the volume of resin from 20-40 to 5-10 vol% results in abundance of inter-grain voids and through permeable pore channels, and in an increase in the rock permeability by two-three orders of magnitude. The single-solution impregnation with the ready mixture ensures lower permeability of the test samples.

The propagation of elastic vibrations in rock samples in compression and under impacts to failure is investigated experimentally. Under impacts, a signal of acceleration was recorded in the samples, and the spectral density was calculated to determine velocities of elastic vibrations. It is found that under increasing load up to a pre-failure value, the P- and S-wave velocities grow, and the S-wave velocity increases by more than 50%. The acoustic Q-factor rises by 70%. The energy of the microseismic emission under pre-failure loads is two times higher than under low loads, and the high-amplitude spectral components generated under pre-failure loading are reflective of large discontinuities being formed.

The article discusses an integrated approach to finding causes of pit wall failure in Zhelezny Mine of Kovdor GOK. Radar monitoring with IBIS provided data for the slope instability prediction. The stability calculation is performed and analyzed for the failed site of the pit wall. It is shown at the adopted strength properties, failure of the upper bench is only possible as its stability factor is less than 1.50. The causes of instability could be the decreased strength of the pit wall as a result of weathering or watering, and failure could occur along a fracture. An industrial building in the close vicinity of the failure site had no influence on the slope stability. The recommendations on finding certain causes of instability are given.

The article describes the lab-scale tests of hydraulic fracturing in the nonuniform stress field. Fractures were created in a system of two and three cross holes made in artificial cubic blocks with the edges 420 mm long. The stress raiser generated at the intersection of the holes facilitates fracturing in the neighborhood. In the tests the maximum compression was applied to a sample in perpendicular to the plane containing the axes of the holes. It is found that in such stress field, the system of three holes stabilizes a fracture in the mentioned plane better than the system of two holes.

The mine shafts in the salt (unwatered) rock mass at the Upper Kama deposit are mostly lined with cast-in-place concrete and reinforced concrete, which should ensure the required load-bearing capacity and water impermeability in host rocks in creep. The long-term observations of the shaft lining in operation revealed some typical patterns of failure induced by the rheological properties of salt rock mass under the action of rock pressure. The technical evaluation of the lining and reinforcement of mine shafts is an integrated checkup procedure including measurements of fractures and areas of corrosive zones/rock falls; updating of actual geometrics of lining from laser measurements; determination of residual strength of lining; mathematical modeling; estimation of integral reliability index of lining. The authors propose a procedure to categorize technical conditions of concrete lining in mine shafts in operation in salt-bearing rock mass in creep. The application of the procedure is described, and the conclusions on the package of repair activities are drawn.

The article describes two single-mass models of a drill string and different methods of bottom-hole treatment: percussion and rotary percussion. The loads created by the piston are transferred to rocks via a progressively advancing bit in the first model and via a rotatable bit in the second model. The drag force applied to the bit is found from the nonlinear dependence on the penetration rate and kinematic parameters which govern the force impact on the rock and its loss of strength: initial blow velocity and rotational speed modulus of the bit. The optimal initial blow velocities are found at the preset blow frequency; they ensure elimination of short-term stick slips in penetration of the bit. For the mentioned cases of penetration, the processes of percussion and rotary percussion drilling in strong rocks are provided with the strict mathematical description. The numerical modeling results are presented.

This study discusses the dependence of blast fragmentation size on field parameters and rock properties. For this purpose, six limestone quarries of productive cement factories of Pakistan were selected, including a total of 19 working bench faces. The field work included determination of rock fragmentation size, field penetration rate, rock mass parameters and blast design parameters. The geo-mechanical laboratory testing program includes LCPC rock abrasivity tests, NTNU/SINTEF drillability tests along with determination of laboratory drilling rate index and physico-mechanical rock property tests. The technique of least square regression was adopted to explain the obtained dependence. Finally, three multiple regression models were proposed for the estimation of rock fragmentation size from the test field and laboratory scale parameters. The quality of developed multi-variable models was statistically validated through statistical performance indicators.

In this study, the rock drillability tests, as well as a comprehensive set of physical and mechanical rock property tests were performed on rock units selected from various localities of Pakistan. Petrography of included rock samples was also conducted for the computation of geotechnical wear indices including Schimazek’s F-value, rock abrasivity index and the Vickers hardness number for rocks. Initially, univariate regression analysis was performed to check the dependence of drillability parameters on physico-mechanical properties and rock wear indices. Significant correlations of drillability parameters with uniaxial compressive strength were found. Similarly, Sievers’ J-value and drilling rate index showed considerable dependence on Schimazek’s F-value. In the next step, multivariate linear regression models of Sievers’ J-value, brittleness value and drilling rate index, based on physical, mechanical and petrographical rock parameters were developed. Finally, the predictability of proposed multiple regression models was validated by employing the statistical performance indices.

The effect of variations in the composition of kaolin and basalt on the geopolymer characteristics was carried out. The drying time was 4 h for cubic samples at 40, 50 and 60 oC and 9 h for cylindrical samples at 70 and 90 oC. The best geopolymer was K4 cylinder at 90 oC, which had a compressive strength of 8.075 MPa. The density of K2 cube geopolymer ranged as 26-1.94 g/cm³ at 60 oC. Silica-alumina compounds dominated the constituent compounds of geopolymer concrete, and the phases formed were quartz, anorthite and muscovite.