On the basis of three selected examples, some problems attributed to the presence of voids resulted from mining operations in already commissioned underground coal mines are discussed. Continuous and discontinuous deformations of the ground surface (sinkholes and subsidence troughs) of anthropogenic origination implicate hazards for the ground surface, even many decades after completion of mining work. Nowadays, when decommissioning and fl ooding of numerous mines happens, ground movements as well as seismic events related to fl ooding of abandoned underground mines can be observed. The fi rst case study draws attention to the problems of effective voids localisation methods as well as the reliability of grout injection operations for road construction purposes. The second case emphasizes a problem occurring often in areas with long and complex mining histories, meaning appropriate determination of origin, process and protective measures regarding occurred ground deformations, or damage to buildings. The third case describes specifi c effects on the surface (shocks and ground surface elevation) generated by the fl ooding of decommissioned mines.
Abstract. Filling the underground voids created during mining extraction of minerals plays a crucial role in different phases of mining operations. A common practice in Polish coal mines is filling the cavings resulted from coal extraction in longwalls for various safety and technical purposes. Moreover, liquidation of redundant underground workings and decommissioning of mines also require filling of large volumes of voids. As the obsolete mining systems with hydraulic backfill have been entirely replaced by longwalls with caving, a need arose for flexible and easily available method for filing of voids. Nowadays, the most frequently applied are mixtures of fly ash and water, which are able to meet a wide range of requirements of specific applications. These objectives may be achieved by the selection of the type of fly ash and adjustment of concentration of solid in mixture in the respect to geometrical parameters of the transport pipeline. These correlations have been demonstrated on the example of measurements conducted on a laboratory pipeline loop for a wide range of fly ashwater mixtures and flow conditions. Measurement results revealed a complex relationship between rheological properties of mixtures and geometrical parameters of pipelines, which strongly influence the distance at which a mixture may be delivered.
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