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The article presents a real case of twin tunnels T4 of the East-West Highway (Algeria) for studying purpose of the effects therein on the soil-structure interaction and the excess pore water pressure on the same by use of a numerical analysis PLAXIS 3D. The results obtained from the Mohr-Coulomb model have been compared with those of Hardening Soil Model for drained and undrained condition. More to the point, it indicates that the soil under undrained condition can produce a significant modification in the normalized internal forces and the moment of lining for the stiff tunnels compared to flexible tunnels.

The authors describe numerical modeling of a growing fracture created between two parallel boreholes in an isotropic medium in the nonuniform stress field. The fracture paths are modeled at various deviations of the initial fracture from the axes of boreholes, spacing of the boreholes and the compressive stress field between them. Physical simulation of hydraulic fracturing is implemented using large-size samples.

A series of laboratory cutter indentation tests were conducted on mudstone samples to study the influence of thermo-mechanical coupling on rock fragmentation. The experimental results show that many micro cracks and pores are formed in the crushed zone of rock sample due to the frictional heat during cutting process. After that, the relationships between specific energy and mesoscopic surface of mudstone samples were analyzed. The results show that the thermo-mechanical coupling is conductive to rock fragmentation. Therefore, thermo-mechanical coupling action in the tunneling process greatly improves the rock breaking efficiency. This study is conducive to extend cutter life, reduce project cost and construction risk in TBM tunnel project.

The authors discuss the application ranges of internal overburden dumping open pit mining. Specifics of internal overburden dumping on gently and steeply dipping beds is given. Internal overburden dumps are classified. The methods and techniques of scaled-up internal overburden dumping by means of efficient utilization of mined-out pit area are identified. The ecological safety of dumping is addressed.

The authors focus on feasibility of reducing deformation of surrounding rock mass around underground structures by means of advanced reinforcement of tunnel headings in claystone. The reinforcement efficiency is estimated in 3D calculations. The factors to influence deformation in rock mass ahead of tunnel faces include: rock bolt length, rock bolting system stiffness and the bolt pattern. An additional factor of concern is the mechanical characteristics of claystone. The implemented research shows the highest influence is exerted on deformation in rock mass by the bolt pattern and the rock bolting system stiffness. The efficient design of advanced rock bolting is determined.

The reference sources on calculation of toxic gas and dust flows in systems of mine roadways are reviewed. It is shown that the calculation should take into account convection and longitudinal dispersion, while molecular and turbulent diffusion in straight-line roadways can be neglected. However, in case of vortex mixture of air in dead-air spaces at junctions in mines, the turbulent diffusion can be comparable with the longitudinal dispersion. The authors propose a calculation formula for the effective longitudinal dispersion coefficient with regard to the influence of air flow velocities in neighbor roadways. The algorithm of nonstationary flow of air pollutants in mine roadways uses the method of splitting by physical processes.

The authors studied theoretically and experimentally the compositions of luminophores in modification of spectral characteristics of anomalously luminescent diamonds to the effect of their recovery. Attachment of a luminophore-bearing composition at the diamond crystal surface takes place owing to the stable aggregation of the diamond, organic liquid and inorganic luminophores by the mechanism of hydrophobic interaction in polar medium. Stability of such aggregates is ensured by intense adhesion of the components having similar surface energy. For diamond and zinc sulfide, the dependence of the wetting angle, generated by the organic liquid drops in the water medium, on the surface tension of the organic phase exhibits the extreme nature. By the coordinate of the maximum of the wetting angle-organic liquid surface energy curve, the surface energy of diamond and zinc sulfide is determined. It is proved that the organic liquids and oil products, which are used as organic collectors and have surface energies similar to the luminophore surface energy, maximize the force of hydrophobic interaction and stability of the diamond-organic liquid-inorganic luminophore aggregate.

The authors undertake a critical analysis of zinc flotation activation mechanisms, namely, ion exchange and electrochemical, and propose a new mechanism of activation of sphalerite flotation by heavy metal ions. Flotation can be activated by physisorption of the collector in the unit event of particle-bubble attachment. The causes of floatability of sphalerite activated by lead ions in the alkali range of pH are disclosed. The characteristic of zinc as a metal-activator consists in high solvability of zinc and xanthate compounds. The conditions of improved floatability of sphalerite after its activation by zinc ions are determined.

The authors describe the studies into nitrate leaching of rare earth elements (REE) from ash and slag. The morphology, texture and structure of surface of ash and slag micro spheres are examined using the methods of scanning electron microscopy and X-ray phase analysis. The experimental efficient parameters of nitric leaching of REE, which ensure the maximum REE extraction at the level of 50.4% include: the temperature of 130 °С, the nitric acid concentration of 7.2 M, the leaching duration of 180 min and the mineral suspension stirring frequency of 500 min^-1. The REE leaching kinetics conforms with the pore-diffusion model of nucleus shrinkage. It is possible to stimulate REE leaching by preliminary treatment of ash and slag by powerful electromagnetic impulses and ultrasound, which ensures intense disintegration of aluminosilicate micro spheres and, as a consequence, provides increased extraction of REE in subsequent leaching by 1.8-18.2%.

The oxidation-induced alteration of properties of sulfide minerals is analyzed. The air-and-gas content and thermodynamic parameters of mine air are experimentally investigated as a case-study of blind roadways in sulfide deposits at a depth of 300-1500 m. The microclimate conditions of sulfide ore oxidation are determined and used in design of two laboratory testing machines with oxidation in a bubbling chamber. It is found that oxidation of sulfides runs more violently in air saturated with steam than in water saturated with oxygen. The tests included two oxidation scenarios: oxygen sorption in surface layer and sulfur oxidation with leaching of metal. On the surface of sulfide ore samples, heterotrophic and chemolitotrophic bacteria which can absorb oxygen from mine air are detected. The highest number of the bacteria is present on the surface of high-grade ore.