Backfilling technology is not always used by mining enterprises, which is conditioned by technological and economic factors, such as the need for high mining rates and costs for the technological processes of transporting backfill materials from the daylight surface to the mined-out space. This concerns the underground mining of hard coal, which is a strategic energy resource, in the mines of Ukraine. This paper aims to study the effect of leaving the waste bottom rocks in the mined-out space of the longwall face without their drawing to the earth’s surface on the geomechanical state of the rocks surrounding the longwall face. The geomechanical assessment of the stress state of the rock mass surrounding the longwall face, when leaving the waste rocks from the seam bottom rocks in the mined-out space, is performed by the finite element method using the Ansys software package. A geomechanical model has been developed and substantiated, which adequately reflects the mining-geological conditions for seam mining within the extraction site, the actual structure and properties of the coal-bearing rock stratum, the parameters of the longwall face and the modified powered support for the processes of leaving the rocks in the mined-out space. The values and patterns have been determined of the decrease in the stress intensity concentrations in the coal-bearing roof mass in the frontal bearing pressure zone and destressing zone with an increase in the ratio of the rock pack thickness to the extracting seam thickness. The relative indicators of the load on the powered support section and the lowering of its roof have been determined by the ratio of the thickness of the rock pack formed in the mined-out space to the extracting seam thickness. The proposed mining method is of significant commercial and research interest for owners of coal mines developing thin coal seams because environmental costs for placing waste on the surface are reduced, and the energy potential of coal is increased due to the separation of waste rocks from coal in underground conditions. The need for a cycle of beneficiation of mined mass is eliminated and the geomechanical conditions of coal mining processes are improved.
Purpose. Analysis of the current state and prospects of Ukraine coal industry development until 2020.Methods. Complex analysis of data regarding mine productivity, coal reserves, mine funds as well as coal consumption and electricity generation has been presented in the paper. The studies of statistics related to geological and extraction thickness in longwall faces are discussed.Findings. The current state of Ukraine coal mining industry and prospects of its development for the period until 2020 are considered. The analysis of Ukraine mine fund conditions is carried out. Statistical data of gross coal production at state-maintained and private mines are given. The reasons for low profitability and coal production decline in the country are considered. Results of the research into ash content of extracted coal, formation and accumulation of mine waste are interpreted. The main promising trends of efficient energy resources use and reduction of environmental impact on coal-mining regions are emphasized.Originality. According to the analysis of the current state of coal industry, several options of its further development are formulated. Practical implications.The presented results can be used to evaluate the investment attractiveness of Ukraine coal mining enterprises.
The paper gives information on the engineering solution concerning the extraction of thin coal seams with partial backfill of the worked-out area. Geomechanical model of coal-bearing rock mass has been substantiated. A technique to carry out computational experiment aimed at the processes of coal-bearing rock mass displacement within a zone of extraction influence has been represented. Curves of rock pressure stress components distribution (i.e. horizontal stresses, vertical stresses, and stress intensity) within the front bearing pressure and worked-out area for traditional methods (if roof is controlled by means of complete rockfall) and for selective mining with partial backfill have been plotted. Relying upon the carried out studies of stress-strain state of coal-bearing rock mass, overall conclusion has been made on the advantage of selective mining with partial backfill from the viewpoint of geomechanics of the rock mass behaviour.
Purpose. Study the movement of waste rock flows in the coal mine technological system and determine the balance of rocks and underground cavities formation from the perspective of the current mining operations development in order to assess the possibility of leaving the rock in the underground area. Methods. Based on the rank order of the Western Donbass mines, a coal mine has been chosen as the object of research in terms of maximum output and ash content. An algorithm is proposed for analytical studies of determining the rock outcrop in the course of stope, drifting and repair operations, as well as the prospective volumes of underground cavities for placing the formed waste rocks per a calendar year. The algorithm is based on the actual state of mining operations and the indicators of the stope and drifting faces of the mine, as well as the achieved modern mining-engineering parameters of the coal seams mining. Findings. It has been revealed that the main supply of waste rocks to the surface occurs as a result of stope operations with rock undercut -39% and underground mine workings -33%. It is proposed to differentiate all waste rock outcropped after mining operations into 2 categories: difficult to dispose of and prospective for disposal. It has been found that underground cavities have enormous potential for stockpiling of all waste rocks, the volume of which is by 2.8-4.8 times higher than the rock volume. It has been revealed that the most rational balance of waste rocks and cavities for leaving the rock in the mine is formed along the С 10 t seam. It has been determined that the full-fledged placement of rocks is limited by the scheduling peculiarities of mining the reserves along the seams, which are made for the complete cave-in technology of coal mining. Originality. For the first time, for one of the Western Donbass mines, the balance of formed waste rocks and potential underground cavities, dynamically changing in time and space, has been determined. Practical implications. The results obtained are useful for engineering new spatial planning solutions for the optimal development of mining operations with the maximum possible rocks stockpiling in the underground area of mines.
Purpose. The research purpose is to study the formation of quantitative-qualitative indicators of mined coal under conditions of dynamic changes in space and time with a new stope mining technology with waste rock accumulation in the underground mined-out area. Methods. The contours are formed for mining low-thickness coal reserves and extracting thicknesses, undercut rock volumes in the stoping and preparatory faces in the conditions of the Heroiiv Kosmosu mine. The average density values of coal, rock layers and wall rocks in the seam within the boundaries of mining contours are determined based on the geological data of wells and mining operations. The graphic basis is executed in the AutoCAD program. A digital spatial model of the С10t seam contours is used, according to the schedule for organizing stope and preparatory operations. The volumes of waste rocks and minerals involved in the formation of quantitative-qualitative rock mass indicators in a given time period are calculated. Findings. It has been determined that during mining of coal reserves from the studied mining area (equal to extraction site), the volume of production and the operational coal ash content in the mining technology with waste rock accumulation averages 376.5 thousand tons and 15.2%, while with traditional technology – 621.3 thousand tons and 46.7%. Nevertheless, it has been proven that in terms of energy equivalent, the value of mined coal using the mining technology with waste rock accumulation is higher by 7.4% than the traditional technology (9.6 TJ versus 8.9 TJ). Originality. For the first time, a mechanism for the formation of operational ash content and energy value of coal has been revealed when combining the processes of drifting operations to prepare reserves from new extraction pillars with associated stope operations into a new selective mining technology with waste rock accumulation in the mined-out area. Practical implications. An algorithm for predicting the operational ash content and quality of coal when using selective mining technology with waste rock accumulation in the mined-out area has been developed, which is important for the technical and economic indicators of coal mines.
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