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The article addresses constraints of hydraulic fracturing application to enhancing preliminary degassing of coal beds. Decisions on geometrizing a hole interval by cemented mixture with cross fracture initiator are presented. An original conveying system for equipment in hole and a robotic hydrofracturing device for hard coal roof and floor are developed. The proposed hydraulic fracturing fluid with low-density proppant allows making fractures ensuring high-rate methane flow.

The article describes a safety control system for water-soluble mineral mining in complicated ground conditions. The system is based on geomechanical interpretation of surface and underground seismic monitoring. Mathematical modeling of water-impervious strata takes into account the whole set of mine-technical and geological factors determined from the seismic observations. It is shown that seismic-geomechanical monitoring allows stress state control in waterproof strata, which ensures prompt decision-making on extra protection and minimizes accident risks.

3D geomechanical model of Vorkuta Mine, Pechora Coal Basin, has been developed and implemented numerically. By the data on dynamic events recorded by stationary seismic stations, tomography of the study object is performed, and velocity of elastic waves is recovered in the illuminated area of the object. The boundary value inverse problem on horizontal external stresses by stress distribution found using empirical relations between elastic wave velocities and stresses determined in the laboratory-scale experiments is formulated and solved.

Stress state of rock mass during fully mechanized longwalling in dislocation zone is analyzed. In focus is the variant of crossing the dislocation zone with disassembling the fully mechanized longwall system and its re-assembling in a new room. Stress redistribution in coal and host rocks when heading approaches dislocation and in post-dislocation mining from the new assembling room is determined.

The authors present the procedure and data of many years-long geodynamic monitoring of the ground surface displacements in Uzelga and Talgan mining areas. Despite similar geological conditions, the difference in the types of the protected objects on the ground surface conditions different variants of the procedure for each deposit. Some points of reference surveying network and observation plugs are re-fixed using the satellite data, digital elevation meter and electronic tachometer, and characteristics of trends in modern geodynamic movement induced by a displacement trough are obtained. The results of the implemented geodynamic activity assessment include vectors of general spatial displacements of observation plugs and curves of compression-tensions and shearing strains. It is determined that rock mass deformation has a discrete mosaic pattern. The conclusions are generalized, and the hypotheses are made on the further deformation of the ground surface.

At mineral deposits and in the intercontinental areas of the Earth, subhorizontal tectonic compression stresses are anomalously high. Many mineral deposits occur within subsurface ring-shaped morpho-formations. The authors solve the problem on stress state in a ring structure at representative stages of its evolution. It is shown that sublateral compression in the ring structure, in particular, at mineable depths, is very heterogeneous, unstable and can considerably exceed stresses due to overburden rock mass weight. The calculated results are compared with the laboratory and in situ data.

In this paper deformation wave is studied on the basis of continuous phase transition theory. Relative shear strain is taken as an order parameter. The potential energy is obtained by analogy with the Ginzburg-Landau expansion of free energy. Hamilton’s variational principle is used to obtain the motion equation by which several types of deformation waves can be modeled. The results show that the proposed model is effective in modeling deformation waves.

The authors offer a simplified two-zone model to describe fluid flow in steady-state horizontal holes with multi-stage hydraulic fracturing and present the analytical solution in order to calculate sizes of hydrofractures. The new procedure to determine size of multi-stage hydrofractures in horizontal holes is tested using field data on China deposits. The calculation results prove the efficiency of the procedure in the determination of steady-state conditions. The procedure can be used in optimization of hydraulic fracturing.

Efficiency of energy-based criterion of volumetric rock destruction in estimation of drilling technology is theoretically validated and experimentally proved in in-situ rotary-percussion drilling in mines in Russia. The criterion is adapted to the performance of various drilling units by means of introduction of empirical coefficients for transformation of drilling energy intake to the relevant energy characteristics of stress rock fracture in face zone. The mathematical description of the criterion of minimum energy intake of rotary-percussion drilling depending on stress state and physical properties of rocks, and on force of rotary-feed mechanism is presented. The authors introduce a new geomechanical notion-factor of topological connection of rocks and give its analytical expression using experimental uniaxial compression and uniaxial tension strength of rocks, required in the design and improvement of rotary-percussion drilling in different geological and geotechnical conditions of mining.

The article addresses the issue of development of a large-diameter (from 500 m and more) rotary drill tool (drill bit) for exploration of placers in permafrost. It is shown that at the contact of drill bits and bottomhole, permafrost thaw takes place with the further adhesion and congelation of the drill tool and hole walls, which degrades coring. The dependence of heat emission at bottomhole on cutter configuration radius on drill bit is determined. The developed design of a drill bit ensures efficient destruction of bottomhole with minimized heat emission, and a prototype drilling assembly is manufactured for large-diameter rotary drilling. The in situ test data are presented.