Mikhail O. Eremin

Reducing the hazard of sudden rock and gas outbursts in coal seams is one of the key problems of geodynamic safety of mining. The paper presents a mathematical model of hydraulic fracturing of roof rocks as one of the key methods for reducing the outburst hazard. Structural features of the working area are studied by means of an example of the host rock strata of seam 3 of the Alardinskaya mine of the Kondomskoye field of the Kuznetsk coal basin. Three-dimensional finite difference analysis and continuum damage mechanics are used to study the influence of the well spacing on the formation of an effective crack network in the hard-to-cave roof during hydraulic fracturing. It is shown that changing the initial well spacing affects not only the formation time of an effective crack network but also the spacing between damage accumulation zones. Hydraulic fracturing of roof rocks from the working face effectively reduces the abutment stress and outburst hazard.

The phenomenon of the strain-rate sensitivity of metallic materials has been a topic of interest since the first mechanical tests at different strain rates were performed. The problem of its theoretical description appeared simultaneously. Despite the significant number of studies covering this issue, it is necessary to rule out a few drawbacks of previously reported models, which is the goal of this work. Herein, an extension of the elastic–viscoplastic model to a generalized state of stress is proposed while aiming to describe the strain rate sensitivity of Armco-iron samples that were pulled in tension within the framework of the finite-difference method. A mathematical model was formulated using equivalent stress and strain, which alleviated the complexity of the relaxation-type constitutive equations. The critical shear stress (CSS) function describes S-type instability with a single equation. The plastic strain rate was calculated based on the well-known Orowan equation, which is related to dislocation dynamics. In addition, the model took the material’s microstructure into account based on the design of a representative volume element (RVE) using the step-by-step packing (SSP) method. The results of the modeling were compared with the available experimental data and were found to satisfactorily correlate with them. The results suggest that the misfit error between the model and experimental data did not exceed 10% in the range of strain rates under study, which is a reliable outcome.

The stability of coal pillars remains one of the most important practical problems for ensuring the geodynamic safety of underground mining. Stress enhancement in the vicinity of openings is responsible for the manifestation of rock, coal and gas bursting, the unsustainability of protective pillars, etc. Stress-induced damage of pillars occasionally causes the breaks of mining due to outbursts. In this work, we apply the finite-difference continuum damage mechanics approach to modeling stress-strain evolution of the rock mass during extraction of adjacent longwall panels of an inclined seam. The numerical modeling allows for explicit account of many factors affecting the rock massif behavior. These are gravity forces, lithology, tectonic stresses, natural discontinuities, geotechnical and mining parameters, etc. When the model parameters are calibrated against the on-site observations, the results of numerical modeling provide a reliable basis for pillars stability assessment. We build a structural model of a rock mass containing an underground working on the basis of a simplified stratigraphy of the Kondomsky deposit, Kuznetsky coal basin, Russia. Based on the results of numerical modeling, the stability of protective pillar is analyzed.

Pillars instability in underground mining of mineral resources remains one of the most acute problem of geomechanics and mining science. Rock bursts and gas bur

In this work, elastic properties of porous zirconium carbide are numerically estimated. Zirconium carbide is widely used as part of metal-ceramic composites. The material in question, being prepared by the sintering, possesses a residual porosity and yields a decrease in effective elastic moduli and strength of material. When developing the multiscale mathematical model of the deformation and fracture processes of ceramic-based composites it is useful to determine the effective characteristics of matrix. The main goal of this work is to determine shear and bulk moduli of porous zirconium carbide matrix. The RVE model is based on experimental data obtained by SEM method. According to SEM patterns the residual porosity is approximately 5%. The numerical modeling of samples loading is carried out in the framework of two-dimensional finite-difference continuum mechanics approach using plain strain formulation. The obtained results indicate the sufficient decrease in effective elastic moduli of ceramics compared to the initial values of ZrC matrix. Obtained estimations satisfactorily correlate with available literature data.