The paper presents an analysis of the advantages and limitations of additional measures to intensify the transportation of the backfill hydraulic mixture flow. The results of the analysis of the conditions for using pumping equipment to move flows with different rheological properties are shown. Generalizations of the methods for influencing the internal resistance of backfill hydraulic mixtures by means of mechanical activation, as well as increasing fluidity due to the use of chemical additives are given. The article presents the results of studies confirming the feasibility of using pipes with polymer lining, which has proven its efficiency in pumping flows of hydraulic mixtures with different filler concentrations. An analytical model of hydraulic mixture movement in the pipeline of the stowage complex has been developed. The trends in pressure change required to ensure the movement of hydraulic mixture in pipelines of different diameters are exponential, provided that the flow properties are constant. The effect of particle size on the motion mode of the formed heterogeneous flow, as well as on the distribution of flow density over the cross-section, characterizing the stratification and change in the rheological properties of the backfill hydraulic mixture, is assessed. An analytical model of centralized migration of the dispersed phase of the hydraulic mixture flow is formulated, describing the effect of turbulent mixing of the flow on the behavior of solid particles. An assessment of the secondary dispersion of the solid fraction of the hydraulic mixture, which causes a change in the consistency of the flow, was performed. The studies of the influence of the coefficient of consistency of the flow revealed that overgrinding of the fractions of the filler of the hydraulic mixture contributes to an increase in the required pressure in the pipeline system.
Underground mining is characterized by the weakening of the bearing rock mass strata competence and the accumulation of mineral waste. The full use of subsurface resources is ensured by the use of technologies with filling voids by hardening mixtures, which requires high-quality raw materials to obtain the required strength. The deficit of the binding component can be filled with the use of granulated slags of blast-furnace process, mill tailings, ash-slags and other wastes. Most often, voids are laid by mixtures with a combination of cement and a binding component. Mixtures with ash-slag additives to cement in an equivalent amount are not inferior to the strength of the mixture only with cement, especially when grinding ash-slag. The properties of stowing rock masses when using composite binding components and inert fillers are controlled by mechanical, chemical, physical and energy effects at the stages of preparation and transportation of hardening mixtures. To obtain the active fraction of cement substitutes, disintegrators are used that apply the inertia forces of materials at a high speed of rotation with an increase in high activity indicators and lower energy costs. The components of hardening mixtures can be the majority of waste from mining and related industries, which is determined experimentally in specific conditions.
At high rates of production face advance, requirements towards reliable operation of undermining drainage holes get raised. The issue of maintaining high intensity of gaseous seams development under naturally increasing gas content, mining depth and capacity of production equipment poses a problem. The greatest threat comes from the loss of hole stability in the bearing pressure affected zone (in front of the face) and in the intensive shift area of overhanging rock corbels (behind the face). Intensification of air leaks due to deformation of borehole channel leads to impoverishment of removed methane-air mixture and an increasing risk to disturb safe aerogas regime in the mining area. The paper describes a mechanism of how coal-face operations affect the state of underground holes and formation of overhanging rock corbels. A typification of basic kinds of borehole deformations is presented. Authors point out critical disadvantages of the most widely-used technological schemes of gaseous seams development under high load on the production face, which hinder normal operation of a gas drainage system. As a result of research, a dependency of shot hole number, as well as the distance between shot hole axes and the borehole, on the stress state of the borehole outline has been defined more precisely. Basing on that, a formula to calculate drilling parameters of the discharge hole system has been suggested. Implementation of these measures will allow to increase the efficiency of underground gas drainage and to maintain growing intensity of gaseous coal seam development.
