Vol 52, No 4 (2016)

The article reports the data of a lab test of directional hydraulic fracturing carried out on a block made of organic glass. A fracture across a hole is created by means of additional shearing stress applied to the hole walls within the interval of the fracture. It is found that seismic emission under hydraulic fracturing appears after the fracture completion.

The approach to numerical modeling of specimen loading considered by the authors using the discrete element method enables describing ability of rocks to accumulate and release elastic energy. The model specimen is a package of particles characterized by viscoelastic interaction with dry friction. The outer layer particles are connected by elastic springs. On the whole, the model specimen is an element of a medium capable of accumulating a part of energy of deformation in the form of internal self-balanced stresses. Numerical modeling of the specimen compression is performed, and the accumulated energy is assessed. It is shown that clusters form in the medium, and sliding along the boundaries of these clusters causes discontinuities in deformation curve. Also, the discontinuities are possible under stress relaxation after unitary dynamic effect on the specimen. There is a good agreement between the numerical and experimental results.

The effect of tensile strength on the tensile fracture toughness of rock like specimen was studied in this paper. Brazilian test was done to determine tensile strength of material. A compression to tensile load transforming (CTT) device was developed for determination of mode I fracture toughness of concrete. Also particle flow code (PFC) was used for validation of the experimental outputs. Three concrete slabs with different tensile strength were prepared for investigation of the effects of tensile strength on the fracture toughness. The samples were made from a mixture of water, fine sand and cement with different ratio. These samples were installed in CTT device. A 30-tons hydraulic load cell applied compressive loading to CTT end plates with a constant pressure of 0.02 MPa per second. Compressive loading was converted to tensile stress on the sample because of the overall test design. The results show Fracture toughness has a close relationship with tensile strength of concrete so it increases with increasing the tensile strength. In constant join length, the angle of crack growth related to normal load was decreased with increasing the grain size. Numerical simulation shows that failure pattern and fracture toughness was nearly similar to experimental results. Finally, it can be concluded that CTT device was capable for determination of fracture toughness of concrete.

Under computational investigation is the process of sequential growth of hydrofractures under conditions of plane strain. The working fluid is perfect and viscous. The authors analyze influence exerted on parameters and trajectories of growing fractures by spacing of the fractures, external compression field, fluid flow rate, fluid viscosity and leakage flow rate.

Loading causes stress concentration around defects in rocks, which induces initiation and propagation of cracks. Physically, external loading shows itself in rocks as acoustic and electromagnetic emission, included infrared radiation. Experimentally, it is found that in specimens of geomaterials under uniaxial tension, temperature is minimum; under uniaxial compression, temperature grows; under triaxial stress, temperature is maximum. It has been succeeded to derive equations for temperature prediction in a material in the zone of main crack as function of failure load. The method to estimate stress state based on the data on infrared radiation in materials is developed.

Under discussion is soil transport by negative pressure generated in horizontal rotating pipeline. Based on the relations between soil batch velocity, soil batch mass and diameter of the pipeline, the authors have developed procedure to determine the limit pipeline length. The rotary velocity of the pipeline is related with its diameter. Reliability of the proposed procedure results is experimentally proved.

Coordination of heating energy sector performance and legal regulations and standards in the area of air protection from toxic substances involves opportunity analysis of limestone supply as limestone is used as deoxidant in the process of sulfur removal from smoke fuses. The problem of supplying heat power plants with limestone reduces to location identification, i.e. selection of an open pit mine offering the lowest cost of transportation. The authors present a single-phase local model for evaluation of decisionmaking in management of limestone supply to heat energy sector plants in Serbia.

The analytical results are given for application of stripping with direct dumping in open pit mines in Kuzbass. It is emphasized that this most productive and the least power-consuming technology loses its weight in the overall content of overburden stripping. The authors propose a method to determine rational boundaries for application area of stripping with direct dumping using slice re-excavation coefficient. The scope of the discussion comprises potential trends of the technology and use of draglines towards enhancement of open pit mining efficiency.

The authors inspect operation of ventilation system in a double-line subway tunnel. It is found that air flow rates required for tunnels and passenger stations differ greatly. For routine operation modes in subway tunnels, the authors evaluate longitudinal ventilation flow chart without station-to-station air chambers, which considerably decreases construction cost of subway ventilation infrastructure. Static pressure fluctuations on outside faces of trains that move in a tunnel in opposite directions are determined. For emergency operation modes of subway tunnel ventilation, under train fire in a tunnel, the authors evaluate a fore-and-aft chart of smoke removal. Toxic emission concentration due to smoke fumes on the way of a breakdown train evacuation is determined. It is proposed to install longitudinal screens in tunnels to ensure safe concentrations of carbon monoxide and carbon dioxide on either way from a breakdown train to a station.

A ventilation improvement index (VII) was developed in an effort to propose an optimal ventilation improvement measure for a designated mine. The index was designed to incorporate both ventilation effectiveness and cost efficiency. To verify the effect of the index, a mine experiencing a ventilation problem was designated and ventilation test and ventilation network analyses were conducted. In the designated mine, 4 areas with ventilations difficulties were detected and an improvement scheme for each area was proposed and evaluation by the ventilation improvement index was carried out. As a result, an optimum ventilation improvement scheme was proposed. The improvement scheme with the highest VII value was incorporated in the design.

The article gives a report on integrated experimental research into targeted change of chemical and phase composition of surface and increase in contrast of physicochemical, electrical and electrochemical properties of tantalite, columbite and zircon under treatment by acid product of water electrolysis—anolyte (pH < 5) and by muriatic solution (HCl, pH 3–3.5). The X-ray photoelectron spectroscopy, high resolution spectroscopy and chemical and electrophysical techniques reveal the mechanism of structural–chemical surface transformation of tantalite, columbite, zircon and feldspar under leaching in acid solutions; this surface transformation mechanism consists in activation of dissolving of iron- and silicate-containing surface films and high-rate oxidation of iron atoms in surface layer of tantalite and columbite, with transition of Fe(II) to Fe(III) and surface destruction of zircon, with formation of oxygenvacant defects of SiO₃²⁻ and SiO₂⁰ type under influence of anolyte.

The data of experimental research into mechanical properties of limestone, hornfels and sandstone cores after treatment by accelerated electrons show that the irradiation changes the strength and deformation characteristics of the tested rocks. In limestone and hornfels, uniaxial compression strength and elasticity modulus decrease, and ratio of P- and S- wave velocities changes; in sandstone tensile strength decreases, while uniaxial compression strength, P- and S-wave velocities and dynamic Young’s modulus grow. Modification of the minerals after accelerated electron irradiation opens ways of creating efficient energy-saving technologies for pre-treatment and processing of complex ores.

The development of a new approach to a distributed information system for bio-diversity appraisal in mining regions, with the use of data storage technologies, cloud computing services and mental processing and analysis of multivariable data is in process. It is suggested to adhere to a cardinally new solution in such system engineering and to add the architecture of such system with NoSQL MongoDB and GeoNetwork components that essentially offload the geoinformation system when retrying special calculations and user requests.

The three-component polyurethane composition is developed to create impervious screens in rock mass by hydraulic fracturing technique. Formulas for working fluids and their injection charts are given. The article describes a lab test and the test data on polymer setting time versus activator concentration and on effect of the fluid composition on the permeability of a porous medium at the limited flow rate of reagent per unit area of the screen.