For years, the Polish hard coal mining has been struggling with the problem of fire hazards in areas with coal residue, mainly in goafs. Currently, a common method of limiting this hazard is the fire prevention involving use of fine-grained hydromixtures based on power generation waste, mainly fly ashes. The hydromixture is introduced into the caving zone created by the advancement of exploitation face and its task is to fill in voids, limiting the possibility of access to the mine air oxygen to a minimum. The first part of the article presents theoretical fundamentals of determining the parameters of gravitational hydraulic transport of water and ash hydromixtures used in the mining pipeline systems. Each hydromixture produced based on fine-grained wastes is characterized by specified rheological parameters that have a direct impact on the future flow parameters of a given pipeline system. Additionally, the gravitational character of the hydraulic transport generates certain limitations concerning the so-called correct hydraulic profile of the system in relation to the applied hydromixture characterized by required rheological parameters that should ensure safe flow at a correct efficiency. This paper shows an example of optimisation of the composition of a selected fly ash-water hydromixture in relation to its capacity for hydrotransport in gravity pipeline installations, as well as the amount of excess water that will always drain from the location of feeding the hydromixture to the underground workings.
Increasing environmental pressure against waste disposal, particularly fine waste surface storage and concern about mining damages have resulted in an increase in the popularity of a fly ash, tailing and binding agent mixture used as compaction grout of roof fall rocks in a gob area of longwalls. Backfilling of voids forming as a result of exploitation with the fall of roof with mixtures containing fine-grained industrial wastes is a common practice in coal mines. It is aimed at achieving numerous technological and ecological advantages as well as at controlling mining hazards. Research on hydraulic transport of fine-grained slurry conducted to date focused mainly on issues related to the analysis of the conditions related to pipeline transportation. The processes concerning the propagation of mixtures within the gob, on the other hand, remain largely unknown. The process of flow of fine-grained slurry through the caving is subject to a series of factors related, among other things, with the properties of the applied wastes and mixtures, the characteristics of the gob as well as the variability of these properties during the flow through the gob and in time. Due to the lack of sufficient knowledge pertaining to the changes taking place in the gob and in the slurry while it penetrates the gobs, no methods allowing for the design and optimization of the gob grouting process have been established so far. The paper presents the selected results of laboratory tests regarding the flow of ash and water mixtures in a model of a gob, pertaining to two selected types of fly ash produced in hard coal combustion, particularly concerning the impact of the type of the ash and the density of the slurry on the effectiveness of the gob grouting process.